Quite the back yard.
Long before I became a avid hiker, I was drawn to the spectacular limestone bluffs on the northwestern edge of the Little Rockies. When I taught in Harlem 40 miles north of here in the mid-1980’s my wife and I occasionally visited friends on their ranch a mile north of the cliffs. Finally one day I walked to the base of the cliffs and found my way to the top. It immediately became one of my favorite places. Since coming out of retirement in mid-December 2019 to teach in near-by Hays, I’ve been able to walk along the cliffs several times.
What’s up with those tilted slabs?
If you’ve ever driven southward across the Fort Belknap Reservation on a summer evening as the tilted slabs of limestone are catching the late-day sunlight, you understand the appeal (see photo below). What hiker wouldn’t want to get up there and have a look? On my three most recent visits to the cliffs I took several drone photos – Those, along with many other photos, diagrams, maps, and Google Earth images are included in the photo tour. I’m not gonna lie – there are some really good photos in the tour, so it won’t hurt my feelings if you go there now. However, if you want to know why there’s a wall of limestone around the Little Rockies, continue reading.
I’m fascinated with the scenic landscape of the Fort Belknap Reservation, so as a science teacher I’ve learned as much as I can about the geology of the area. Here’s what I know about the wall . . . The cliffs are made of nearly vertical layers of Madison limestone, formed from sediment that was deposited during the Mississippian Period about 320-360 million years ago. Thick deposits of corals, shells, and other forms of calcium carbonate accumulated on the floor of a shallow tropical sea when this part of Earth’s crust was much closer to the equator. The Madison limestone makes a major contribution to the scenery of Montana – The Gates of the Mountains, the Rocky Mountain Front, Lewis and Clark Caverns, Sluice Boxes, and Bighorn Canyon are all made of (entirely or partially) Madison limestone.
The rest of the story.
The sediment was deposited in horizontal layers, eventually became rock, and was covered by younger layers, which also became rock (sandstones and shales). Then about about 60 million years ago magma worked its way toward the surface, causing the layers to be domed upward. The magma hardened, becoming the igneous rock found at the core of the mountain range. The doming occurred in an area about 15-20 miles in diameter. Over time, most of the limestone and other layers above the igneous intrusion eroded away, leaving only the steeply-tilted edge of the limestone dome that forms the cliffs shown in the photo and other similar outcrops around the perimeter of the Little Rockies. Hey! Thanks for sticking with me! Now go enjoy the photo tour. 🙂
Below: This map marks hikes that have been featured on bigskywalker.com so far, including several in Glacier Park – Select full screen to expand, zoom in for more detail, or click on a marker for a link to the post.