Sunday, April 6, 2014

Practical considerations and hazards

If you do choose to explore Twin Cities geology beyond the most convenient couple of places, it is worth knowing something about the terrain. Most practicalities are the same as you would use for any hiking trip: sturdy boots, sunscreen, insect repellent in the buggy times of year, a hat, and so forth. I recommend long pants and sleeves, to protect your arms and legs from banging against things and to give you less to worry about in terms of bloodsucking multi-legged friends, but I realize that this can get extremely uncomfortable in the summer, when the atmosphere transitions from hot and humid to hot and gelatinous. At any rate, choose clothes that you wouldn't mind getting ripped, roughed-up, or coated in mud. Have water on hand, too.

Keeping safe is usually a matter of common sense: stay away from rock walls and the edges of drop-offs, don't go hiking when the ground is wet or covered in wet leaf litter, remember when dealing with slopes that it's usually easier to go up than to go down (and don't put yourself in a situation where you can't do either), and never trust a pile of loose stone.

Most places will have one of two basic configurations: you are on a trail with a steep bluff either below you or rising next to you. If you are above the Platteville, the bluff is below you; this is what you see if you are on the highest level of goat trail between Summit Avenue and the Ford Bridge along the river in St. Paul. If you are below the Platteville, the bluff is next to you and includes some thickness of the St. Peter; this is usually what you see along the Winchell Trail, the bike paths in the Fort Snelling and Mendota areas, or at Hidden Falls. A less common variant puts you at more or less the level of the St. Peter–Glenwood contact, with the Platteville right next to you. If you are above the Platteville, the basic issue is making sure you don't go over it, because you're more or less guaranteed a fall of 30 ft (typical Platteville thickness), usually followed by another 30 or so feet of steep St. Peter (to say nothing of the fact you've probably taken some Plattteville with you, and it's solid, heavy stone). Therefore, stay away from the edge, and let the trails dry.

You'd never know this wasn't load-bearing from above (Crosby Farm Park).
Another thing to note in regards to the Platteville is its habit of vertical jointing. This can be readily seen on the natural platform at Shadow Falls. Eventually, the rocks will give way along the joints.

If you're next to or below the Platteville, the main concern is falling rocks. Sometimes, the hazard is obvious:

Washington Avenue bluffs: this is Nature's subtle way of saying "You fool! What are you doing?"
Gravity is usually the major hazard, but not always through falling rocks. Take the following, in the ravine at Shadow Falls:

This is a slope with a coating of eroded Decorah Shale. Provided you have wisely avoided it when wet (if not, you are walking an inch taller from the clay stuck to your boots), you may decide to climb up and check for interesting things to photograph (you may not have known it, but Shadow Falls is a city park and you're not supposed to take fossils). Plan carefully, because it's a lot easier to go up than to go down. If you don't think you get down the slope without falling, just keep going up. The trees are your friends here, but the rocks aren't, as I discovered once (fortunately, I was already almost at the top). Places with knobs of St. Peter Sandstone are also like this, except the sandstone tends to be smoother and steeper and there are no trees. It's remarkably easy to get yourself into places on the St. Peter where you wonder how in the world you're going to get down.

Talus offers one more potential difficulty. It's not uncommon for Platteville outcrops to feature big piles, and it's often tempting to climb around to look for chunks with interesting exposed fossils. If you decide to do so, it is imperative that you keep track of your footing. Blundering around on talus is a great way to accumulate limb injuries.

Big Rivers Regional Trail

Near the overlook north of Ford Bridge in St. Paul; it looks safer than it is
Finally, remember that these areas are usually parks of one stripe or another, so you'll be sharing the environment with all kinds of people. Hikers, joggers, cyclists, picnickers, families with small children (try not to give them any ideas by being halfway up a cliff), bird watchers, dog walkers, teens and college kids out to have a drink or a smoke, couples sharing a romantic interlude, homeless people, and others can all be found any given summer day. As a rule, the more privacy that someone wants, the more secluded the area.

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