What do Delaware, Hawaii, and Rhode Island have in common?

Answer: They are the only three U.S. states for which I can't find a record of a mastodon or mammoth.

Hawaii is not exactly a surprise. Certainly proboscideans can swim, but if you want a large mammal that can swim halfway across the Pacific Ocean without dying, it's going to look and function suspiciously like a cetacean instead.

Delaware and Rhode Island, on the other hand, doubtless had mammoths and mastodons tromping over them at some point, because they're surrounded by states (and submerged coastal plains) that have their fossils. They're just both small states not blessed with the most helpful geology, and mantled by urbanization. Rhode Island gets an additional strike from being subjected to glaciers. Someday the fossils will turn up, though. Maybe there's already something; maybe somebody has a funny-looking doorstop they found in 1973 and never paid much attention to, or there's a notice in a local paper published in 1989 about a couple of campers who found a tooth and turned it over to a local historical society, or somebody will hop into the comments of this post and say, "Hey, ya numbskull, ya missed this!"

Now, the nitty-gritty: every once in a while I'd wondered how many states have records of mammoths or mastodons, and occasionally puttered in a source or two. This time I decided to be more thorough. I checked the Hay inventories, Neotoma (which has the old FaunMap contents), and the Paleobiology Database for starters. These three together narrowed down the list of absences to Delaware, Hawaii, New Hampshire, and Rhode Island. If you're curious: Hay didn't have mammoths or mastodons in those four plus Maine and basically omitted Alaska, but had all the rest plus the District of Columbia; Neotoma was missing the four plus Alabama, Mississippi, North Dakota, Vermont, and D.C.; and the PBDB was missing the four plus Connecticut, Louisiana, Massachusetts, Maine, New Jersey, North Dakota, Vermont, and D.C. This is why it's important to check multiple sources; no one source has everything.

Putting aside Hawaii, that left Delaware, New Hampshire, and Rhode Island to check out. Now was the time to drill into the resources of various search engines and museum databases/iDigBio. For the record, I leaned on Google Scholar, Google Books, and the news tab of regular Google (not Google News), with various permutations of "mammoth", "mastodon", "Mammuthus", and "Mammut" plus a state, with additional terms as necessary to knock out particularly obnoxious false positives. This eliminated New Hampshire, which now has a record from a find on land [note, 2026/06/02: nope, see comment below] after a couple of teeth found nearby offshore. For a short time I'd thought I'd found one for Delaware, thanks to a short piece in the Winter 1994 issue of "First State Geology" (p. 3). The article mentioned that Jeremy Cloutier of Milford had donated a mastodon tooth to the Delaware Geological Survey, but the tooth derived from offshore clam dredging and therefore doesn't count for our purposes. So, for now, we're still at Delaware, Hawaii, and Rhode Island. (Still a few field days 'til Christmas, if you're feeling like pulling off a Christmas miracle!)

"Archie", the world's largest mounted Columbian mammoth skeleton, on display in Elephant Hall, University of Nebraska State Museum.

Catching up with NPS proboscideans

I had occasion recently to review some of the records in the 2020 National Park Service fossil proboscidean inventory (Mead et al. 2020), so I thought it would be useful to produce an update on the roster of parks, National Natural Landmarks, and National Historic Landmarks that we included at that time.

Fossils at Airports

This year's annual Society of Vertebrate Paleontology meeting was held in Cincinnati, and I was quite pleased to be greeted in Concourse B of Cincinnati/Northern Kentucky Airport by a mastodon skeleton.

This seemed like a good omen.

This is hardly the only airport to have fossils. Sometimes they are part of the building stone; at Minneapolis–St. Paul International Airport, for example, you can hardly walk around without seeing fossils in the (non-local) flooring stone. Most of the fossils are bits and pieces of shells, but there are some nice coiled cephalopods, and if you have time they're certainly worth a pause. (It would be fun to do a thorough photographic inventory, but I imagine it would probably have to be explained so as not to appear nefarious.)

Two cephalopods with part of my foot for scale.

A generous assortment of large fossil debris.

In other cases the fossils are on display, as at Cincinnati. One of my favorite examples is the Brachiosaurus at Chicago O'Hare. I've become fairly familiar with this mount over the years since I first saw it on the way to Mongolia, as O'Hare has been practically a required stop on my trips east from MSP.

On this visit in 2019 the brachiosaur was decked out in Chicago Bears livery for the NFL's centenary.

Back to Cincinnati. (Well, not literally; the airport is actually across the Ohio River in Kentucky.) In the mastodon photo above another skeleton can be seen in the distance. I'd been in a hurry when I arrived, so I hadn't explored farther, but made it a point to do so when I departed. It turned out there were five more mounts in the concourse, which makes me wonder if there were any in Concourse A. The animals chosen for exhibit are all typical Ice Age fauna of the area (in fact, all have been found at Big Bone Lick not too far down the river). One notable absence, if only by name, was the giant beaver Castoroides ohioensis, so I kind of hope there were more in Concourse A.

Cervalces scotti, the "stag-moose"; think of a moose with fancier antlers.

A dire wolf pursues an extinct peccary.

A giant ground sloth; the mounts are convenient to walk around, particularly nice for appreciating the unusual anatomy of this animal.

A Smilodon smiling.

Proboscidean update: the Williamsburg mammoth (or mastodon)

Leaving titanosaurs aside for the moment...

A couple of times now, I've featured inventories of National Park Service proboscidean fossils: mammoths, mastodons, and so forth. One of the records that's been stuck as questionable is an 1811 report from the area of Colonial National Historical Park. To quote from the most recent published assessment, in Mead et al. (2020):

“The Williamsburg-area mastodon was first reported in 1811 (Anonymous 1811). The details vary from report to report, but apparently the bones were found 10 km (6 mi) south (Anonymous 1811) or east (Mitchill 1818) of Williamsburg on the south bank of the York River. It is unclear where the former location would be, but the latter is potentially within COLO [Colonial National Historical Park], in the vicinity of Bellefield Plantation and the mouth of Indian Field Creek. Anonymous (1811) reported that the site was a few yards within high water near the home of Gawin Corbin. The fossils include 2 tusks, 2 vertebrae, 1 pelvis, 1 femur, and partial mandibles with 7 associated teeth (Mitchill 1818). Given the presence of molars, it is surprising that Mitchill (1818) identified the specimens as mammoth, yet Hay (1923) reported them as a mastodon (Mammut). Hay (1923) reported that the bones were probably destroyed in the 1859 fire at the College of William and Mary. Clark and Miller (1912) refer this specimen to the Pleistocene of the Talbot Formation (a now-obsolete name)."

I and others have made attempts over the past few years to determine who the Gavin Corbin in question was and where his property was located, most recently as part of the Colonial National Historical Park paleontological inventory currently being reviewed. The primary issue has been the numerous Corbins who have lived in this region, including multiple Gawin Corbins. In such a case, sometimes you have to trust in serendipity, and I can now state that I'm practically certain the answer is at hand. The man in question is Gawin Lane Corbin (1778–1821), and the property is the “Kings Creek” plantation, now within the U.S. Navy's Cheatham Annex just north of the Colonial Parkway.

This was the kind of thing where it was helpful to have some experience in genealogical research. It wasn't enough to have a good candidate for the name; there also had to be a way to track the location. In this case, "Kings Creek" has a lengthy history, beginning as "Utimaria" in 1630 and passing through various hands until being sold to Corbin's father in 1790 (Tyler 1894; Anonymous 1913). Later the area was known as Penniman, and eventually the Navy's Cheatham Annex. Importantly for us, we also know that the Ringfield and Bellefield (or Bellfield, or Belfield) plantations were active in the same time frame as the fossil discovery, on what is now the NPS side of Kings (or King’s, or King) Creek. With this knowledge, we can be certain than any mammoth or mastodon found near the home of Gawin Corbin on the York River shore was found in what would now be part of the Cheatham Annex, and therefore near but not within the historical park. (On the other hand, if anyone from the Annex is reading this, it looks like there's a mammoth or mastodon in your history.)

Presumably Corbin had some idea of the significance of the find for it to have been collected in the first place. He was certainly in a position to have been exposed to discussion of such fossils, having social standing and a college education (William & Mary alum; Anonymous 1922) at a time when fossils of mammoths and mastodons held an unusual fascination beyond their scientific value.

Near the mouth of King's Creek, looking north toward Penniman Spit.

References

Anonymous. 1811. Curious discovery [elephant bones from York River, Williamsburg, Virginia]. Philadelphia Repertory 2:87–88.

Anonymous. 1913. Notes from the records of York County. William and Mary College Quarterly Historical Magazine 22(2):73–89.

Anonymous. 1922. The Corbin Family (continued). The Virginia Magazine of History and Biography 30(4):403–407.

Clark, W. B., and B. L. Miller. 1912. The physiography and geology of the Coastal Plain province of Virginia. Virginia Geological Survey Bulletin 4:13–222.

Hay, O. P. 1923. The Pleistocene of North America and its vertebrated animals from the states east of the Mississippi River and from the Canadian provinces east of longitude 95 degrees. Carnegie Institution of Washington, Washington, D.C. Publication 322.

Mead, J. I., J. S. Tweet, V. L. Santucci, J. T. Rasic, and S. E. Holte. 2020. Proboscideans from US National Park Service lands. Eastern Paleontologist 6:1–48.

Mitchill, S. L. 1818. Observations on the geology of North America; illustrated by the description of various organic remains found in that part of the World. Pages 319–431 in G. Cuvier. Essay on the theory of the Earth, with mineralogical notes, and an account of Cuvier’s geological discoveries, by Professor Jameson. Kirk and Mercein, New York, New York.

Tyler, L. G. 1894. Notes by the editor. The William and Mary Quarterly 2(4):230–236.

A Star-Spangled Mastodon?

When I wrote about the NPS fossil proboscidean inventory, you may recall that I mentioned there was one Eastern record I wished I could have confirmed. I thought it was only fitting to shine a spotlight on it in conjunction with the anniversary of the event that made the park unit in question famous.

National Park Service proboscideans revisited

You may recall that a few years ago I ran a post with a map summarizing proboscidean records in National Park Service areas. Sometimes these things take on a life of their own. I'm happy to share with you Mead et al. (2020), a fleshed-out compendium of fossil proboscideans from National Park Service units, affiliated areas, and National Natural Landmarks and Historic Landmarks. The citation is:

Mead, J. I., J. S. Tweet, V. L. Santucci, J. T. Rasic, and S. E. Holte. 2020. Proboscideans from US National Park Service Lands. Eastern Paleontologist 6:1–48.

Gomphotherium osborni in Elephant Hall, University of Nebraska State Museum. You may not realize it, but proboscidean fossils are very common in Nebraska. We haven't had a gomphothere photo yet, so it seemed appropriate.

The project had a serendipitous beginning; my supervisor Vince Santucci and I occasionally produce inventories of fossil groups from NPS lands, as thematic inventories. We'd been kicking around ideas for our next such inventory and put the proboscideans on the short list. At SVP 2018, Vince got in contact with Jim Mead of The Mammoth Site of Hot Springs about the planned Quaternary section of the Grand Canyon National Park report. He also brought up the proboscidean inventory, Jim was interested, and all that was left was assembling notes, writing, and revising (you know, the easy part). (One of the side effects of the work I do is that I have a very eccentric CV. Of course, that's one of the things I love about my work, getting to work with a bit of everything.)

Despite the ponderous subjects, this is not what you'd call a "heavy" paper. It's a compendium of various reports. Having said that, many of these reports we compiled are either published only in a very limited way elsewhere, or are unpublished. These include internal park reports, collections information, and other such documentation. We cast a very wide net to be as comprehensive as possible; as such, you might think that some of the things we included are very marginal. There's everything from mammoth bonebeds to a tooth fragment found in a cave at Grand Canyon NP. There's dung-filled caves and several track sites. There are artifacts carved from ivory from Alaska. There's even a mastodon tooth found in Philadelphia that might have belonged to Benjamin Franklin.

In terms of geography, the occurrences are spread throughout the country, but there is a definite bias to the West. This is probably due in large part to factors outside of the actual distribution of proboscideans: there aren't as many large parks in the eastern US, many of the park units are in urban areas, and many of them were established for human events that occurred in the past couple hundred years. (There's one eastern record I wish I could have confirmed. Another time, maybe.) Most of the records are for Pleistocene mammoths and mastodons, although there are a few going back into the Pliocene and Miocene. I certainly now have a much greater appreciation for the fossil record of the Niobrara National Scenic River corridor.

Did we get everything? Well, we cast a wide net, as I said, but I would not be surprised if we missed things, especially given that many of the reports we did include are of limited circulation; surely there are others lurking in file cabinets and in the recesses of hard drives? In fact, I'm hoping this will lead to people pointing out records we missed. If there was an update in ten years, I would absolutely expect that there would be additions from things we overlooked. In particular, our records of fossils in National Natural Landmarks and National Historic Landmarks are in an early stage of development, making these the most logical candidates for new information. Anyway, if you're curious about proboscideans in the Parks, we've got you covered!

Stegomastodon mirificus, same venue. Despite the name, it's not a close relative of mastodons (and certainly has nothing to do with Stegosaurus!); it's a later gomphothere.

Stillwater tusk(s): Minnesota's first

Stillwater, Minnesota is not the kind of place that comes to mind when thinking about good elephant country. If you've never been there, there's a bit of a drop from the top of the St. Croix Valley to the river (the map coming up will make this clear). Furthermore, Stillwater is not noted for its broad floodplain, so a proboscidean wouldn't have much space if it did come down. However, the deep valley of the St. Croix itself is of geologically recent vintage, a parting gift of the most recent ice age sending meltwater through an area marked by billion-year-old faults. This is all a long-winded way of saying that compared to today, it would have been much easier to have mammoths and mastodons wandering around the future area of Stillwater right after the ice had cleared out, only where they were wandering wouldn't have looked very much like how it looks like today.

In fact, what appears to be the first documented find of mammoth or mastodon fossils in Minnesota was made in Stillwater in 1856 (Anonymous 1860; Stauffer "1945"). The find was briefly mentioned in a description of the Minnesota Historical Society ("Already we find it its museum the remains of the first mastodon found in the State, presented by A. [Abram or Abraham] J. Van Vorhes, esq., of Stillwater"; Anonymous 1860), but a fuller account would not be made until Newton Horace Winchell took an interest in it.

According to Winchell, who met with Van Vorhes, the find came from coarse river gravel (actually the base of a bed of fine sand 30–40 feet thick [9–12 m] according to the included stratigraphic section) "far above the present river, but within the main valley" and consisted of a single mastodon tusk (Winchell 1878). Obviously, as an isolated find there's really no way to be certain where the tusk was when its services were no longer required by its owner, but we take our tusks where we find them. (There are differences between mastodon and mammoth tusks, but I don't know if these were known in the mid-1800s, or if this is just a case of "mastodon = generic American proboscidean".) Van Vorhes also reported pottery fragments at the top of the sand bed. Eight feet (about 2.5 m) of the tusk went to the Academy of Sciences of St. Paul (Winchell 1878), and would have been lost in the 1881 fire (mentioned previously).

Winchell also included an extensive quotation from Van Vorhes, who reported multiple tusks "were found about eight or ten feet [about 3 m] above the base of the hill: the hill at this point rises at an angle of about 45°. After excavating in the base of the hill on the grade of Myrtle Street about 37 feet [11 m], the tusks were found, consequently 37 feet below the surface. At this point the hill was about 90 feet high [27 m].

The crockery I found some thirty feet [9 m] farther into the hill and some six or eight feet [about 2 m] higher in the strata. This hill is a continuous tongue of land lying between the Florence mill stream and a spring run. The two streams run parallel and some 350 feet [107 m] apart. The hill is so steep on the Florence mill side as to be inaccessible except by clinging to roots and brush growing on it. The material at the base is sand and small gravel. Where the tusks were found the strata were pure sand ten or twelve feet thick [about 3 m], exhibiting clearly the direction of the current in an eastward inclination one or two degrees."

Leaving aside the question of one tusk or multiple tusks, the location of the find can be reasonably well established from Van Vorhes’s recollections (refreshing for a mid-19th-century find!). The Florence flour mill is long gone, and was not built until 1872, so Van Vorhes was using the then-current geography to describe the 1856 situation. However, as mentioned in the linked article, "The water for the mill was brought down from a dam located where the Pitman House once stood, now the northern portion of Trinity Lutheran Church, and supplied by a brook from McKusick’s Lake." The church is adjacent to Myrtle Street between 3rd Street N and 4th Street N, and a valley can be traced from this area to the lake. The "spring run" seems most likely to be related to a valley to the south, but the present-day distance is much greater than 350 feet. Given that Van Vorhes was an experienced surveyor, it's unlikely he would have been off by hundreds of feet or more; it seems more likely to me that the critical area has been so heavily modified in later years that the 1856 watercourses have been obscured or obliterated. My guess is that the find was made within 500 feet (150 m) of the present location of the church.

This map (helps to click) shows several of the landmarks mentioned above. As I said, I think the find was made in the vicinity of the modern church. (Here's a plug: I've found the Earth Point topo map overlay for Google Earth invaluable!)

The location was retransmitted incorrectly in Hay (1924:44), who placed it in Browns Creek. I suspect this stems from a misreading of a later report by Winchell. Winchell (1888:397) stated "In the fall of 1872 the writer [Winchell] first visited Stillwater, and in company with Mr. Abram Van Vorhes examined the deposit of tripoli in the valley of Brown's Creek. At the same time Mr. Van Vorhes pointed out the drift bank in which he had found ancient pottery and the remains of the mastodon." It's not hard to see how a reader may have come to the conclusion that the "drift bank" was in Browns Creek. This creek, though, is on the north side of Stillwater; Highway 96 borrows part of its valley. It is approximately 1.4 miles (2.3 km) north of the actual area of the find.

The loss of the specimen relegated it to a paper curio. Winchell returned to it once more, in 1910, which is notable because he hedged on the mastodon identification, acknowledging it could have been an "elephant" (mammoth). Aside from Hay (1924), the only other place it seems to have appeared in the literature since Winchell is Stauffer's inventory of Minnesota's Pleistocene fossils (usually given as 1945, but at least 1948). Winchell’s report is #17 in this publication, and Stauffer classified it as "Elephas sp.", which translates as "some kind of proboscidean". Stauffer included another Stillwater find, #6, a tusk found in terrace gravels “in the edge of Stillwater” at an unspecified time. With such little information, it is impossible to say anything else about it.

[An unrelated closing note: I really ought to plug the Geological Society of Minnesota more frequently for local readers; for example, there was a talk this week on Cretaceous fossils in Minnesota. This would have been the normal closing session of the spring lecture series, but an opportunity arose for the GSM to co-sponsor a presentation by Peter Brannen on "The Ends of the World", his book about extinction events, Monday, May 20th (see flyer below for more details). The fall lecture series will start up in September. The GSM staffs a booth during the State Fair in the Education building if you'd like to stop by and chat in person. Lectures are free and open to the public.]

Here's a flyer for the upcoming talk. Note: "Blue Line" should be "Green Line".

References

Anonymous. 1860. Minnesota. The Historical Magazine 4(5):141–142.

Hay, O. P. 1924. The Pleistocene of the middle region of North America and its vertebrated animals. Carnegie Institute of Washington Publication 322A.

Stauffer, C. R. “1945” [at least 1948 based on dates in the article]. Some Pleistocene mammalian inhabitants of Minnesota. Minnesota Academy of Science Proceedings 13:20–43.

Winchell, N. H. 1878. Primitive man at Little Falls. Minnesota Geological and Natural History Survey Annual Report 6:53–65.

Winchell, N. H. 1888. The geology of Washington County. Pages 375–398 in N. H. Winchell and W. Upham. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 2. Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Winchell, N. H. 1910. Extinct Pleistocene mammals of Minnesota. Bulletin of the Minnesota Academy of Science 4:414–422.

The Pacific Mastodon

Mastodons have been in the news this week, thanks to a new paper by Alton Dooley et al. that makes a case for distinguishing a new Pleistocene species, Mammut pacificus, from the familiar Mammut americanum. The paper is freely available, so give it a look if you're interested in the technical side of fossil proboscideans (mammoths, mastodons, elephants, and friends). If you're interested but not quite up to speed on the details, there's also an in-depth interview with the lead author.

The skull of the type specimen of M. pacificus, Figure 1 in Dooley et al. 2019. From the caption: "Cranium in: (A) dorsal, (B) ventral, (C) left lateral, (D) right lateral, (E) posterior, (F) distal end of left tusk (I1), lateral, and (G) right tusk (I1), lateral view. Teeth include left and right M2–M3. (A–E) are images of a resin cast of the holotype cranium on exhibit at the Western Science Center. All images are orthographic views of photogrammetric models. Scale = 10 cm."

Although mastodons and mammoths are among the most familiar extinct animals, our understanding of their species is still fairly hazy. For those of you who are unfamiliar with the issue, the short answer is that paleontologists historically loved to name proboscidean species. The long answer is too long for a post, but there's a little 1,800-page two-volume monograph by Henry Fairfield Osborn that may provide some illumination. You can read and download the volumes from the Biodiversity Heritage Library (both) and Internet Archive (1, 2). Two caveats for the reader: both volumes are large files (88 and 103 mb, respectively), and Osborn had some* ideas about taxonomy and evolution that have not quite stood the test of time. The 1920s and 1930s were a splitting time, and Osborn could split with the best of them. Over the following decades researchers have gradually settled on a shortlist of a few species and genera, but there are still a lot of questions, and given the results from the original binge of species-naming there hasn't been much of an appetite for creating more.

*By "some" I mean "all of them".

Western North America appears to have been mammoth country; mastodons are not particularly abundant, with many finds only coming in the past couple of decades. Dooley et al.'s project started with a mastodon found at Diamond Valley Lake West Dam near Hemet, California. This mastodon, now on display at the Western Science Center and known familiarly as "Max", has small third molars for its size. (As the interview relates, this fact only became apparent when Dooley was working on exhibit text, and then the project grew from there.) The authors began making comparisons to other mastodon specimens. What they concluded, after several years of work, was that mastodons from California and southern Idaho shared a small suite of characteristics unlike the more familiar mastodons of eastern North America. Aside from the small third molars, these include six fused sacral vertebrae (usually five in M. americanum), femora with relatively thicker shafts, no mandibular tusks (M. americanum sometimes has tusks in the lower jaw), and males with relatively thinner tusks at the base.

Figure 33 from Dooley et al. 2019. The caption there reads "Red circles mark all known M. pacificus localities, while blue circles mark the M. americanum localities that produced teeth used in this study and represented in Table S2. Note that while there are many additional M. americanum localities that were not included in this study and that are not indicated on the map, there are no known M. americanum localities in California. The M. americanum locality in Oregon is a non-diagnostic specimen that was included as M. americanum in this study, but that could represent M. pacificus."

Dooley et al. found not only that all of the mastodons that could be studied from California shared these characteristics, but that the differences extended well into the Pleistocene, into the Irvingtonian land mammal stage. The mechanism for species separation would most likely be ecological: mastodon fossils are particularly rare in the mountain and desert country that intervenes between California and the rest of North America, and there may simply have not been enough suitable suitable mastodon environments in that region to keep the California population connected to the eastern population. In recognition of this distinct population, Dooley et al. coined the name M. pacificus, the Pacific mastodon. Moral of the story? Keep looking at your fossils, even if it's something seemingly well-known; you never know when something unusual might turn up.

References

Dooley, A. C., E. Scott, J. Green, K. B. Springer, B. S. Dooley, and G. J. Smith. 2019. Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America. PeerJ 7:e6614. doi:10.7717/peerj.6614.

Marshalls Creek Mastodon

This is something of an apology. I gave a paleontological presentation for the folks at Delaware Water Gap National Recreation Area last September, and after I finished someone brought up the Marshalls Creek Mastodon. I'd been focusing on other topics, so the mastodon hadn't made the cut (for shame on my account!). I am now remedying that omission. For the rest of you who haven't been introduced to the fossil in question, you can also find accounts in Hoff (1969, 2001), which are my primary sources. The Monroe County Historical Association also has a brief online account.

Mammoth roundup

A couple of new publications concerning mammoths in National Park Service units have crossed my desk recently, so it seemed like a good opportunity to say a few further words on behalf of extinct proboscideans in the National Parks. I present to you first the finely wrought map below, which shows the various parks where body fossils of mammoths, mastodons, and their friends have been reported. At press time, there were 37 parks, monuments, and so forth with confirmed records, and another six with possible records (cases where the locality is not clear). This map has the novelty of differently colored and shaped symbols, which aside from providing a splash of color, show a preponderance of mastodons in the northeast and mammoths in the southwest. I've relied on the literature and such, so there's definitely the chance that some of the "mammoths" are mastodons, and vice-versa. Most of these records are from the Pleistocene, but there are a few that are older; notably, John Day Fossil Beds National Monument and Niobrara National Scenic River have both gomphotheres and mastodons of pre-Pleistocene age. The great majority of the mammoth reports in the lower 48 are likely Columbian mammoths, Mammuthus columbi (M. exilis of Channel Islands National Park being a notable exception), but given the ambiguities in North American mammoth taxonomy, I figured it wasn't worth the time to try to split them up.

I use the base map a lot, don't I? Definitely a "click to embiggen" this time, to enjoy the various colored symbols. Inventory of points: 1) Nez Perce National Historical Park, multiple states; 2) John Day Fossil Beds National Monument, Oregon; 3) Hagerman Fossil Beds National Monument, Idaho; 4) Lava Beds National Monument, California; 5) Golden Gate National Recreation Area, California; 6) Death Valley National Park, California–Nevada; 7) Tule Springs Fossil Beds National Monument, Nevada; 8) Lake Mead National Recreation Area, Arizona–Nevada; 9) Mojave National Preserve, California; 10) Channel Islands National Park, California; 11) Santa Monica Mountains National Recreation Area, California; 12) Joshua Tree National Park, California; 13) Noatak National Preserve, Alaska; 14) Kobuk Valley National Park, Alaska; 15) Bering Land Bridge National Preserve, Alaska; 16) Denali National Park and Preserve, Alaska; 17) Yukon-Charley Rivers National Preserve; 18) Arches National Park, Utah; 19) Glen Canyon National Recreation Area, Arizona–Utah; 20) Grand Canyon National Park, Arizona; 21) Wupatki National Monument, Arizona; 22) Colorado National Monument, Colorado; 23) Florissant Fossil Beds National Monument, Colorado; 24) Great Sand Dunes National Park and Preserve, Colorado; 25) Bent's Old Fort National Historic Site, Colorado; 26) Salinas Pueblo Missions National Monument, New Mexico; 27) White Sands National Monument, New Mexico; 28) Lake Meredith National Recreation Area, Texas; 29) Big Bend National Park, Texas; 30) Amistad National Recreation Area, Texas; 31) Waco Mammoth National Monument, Texas; 32) Padre Island National Seashore, Texas; 33) Big Thicket National Preserve, Texas; 34) Buffalo National River, Arkansas; 35) Vicksburg National Military Park, Louisiana–Mississippi; 36) Niobrara National Scenic River, Nebraska; 37) Mississippi National River and Recreation Area, Minnesota; 38) Mammoth Cave National Park, Kentucky; 39) Potomac Heritage National Scenic Trail, multiple states; 40) Valley Forge National Historical Park, Pennsylvania; 41) New Jersey Pinelands National Reserve (affiliated), New Jersey; 42) Fort McHenry National Monument and Historic Shrine, Maryland; 43) Colonial National Historical Park, Virginia.