Montana’s Ocean View

The National Weather Service’s winter storm warning for today reminded me of some research I did a while back about Montana’s tropical past. So, brew a cup of something warm, plan a cross-country ski trip for this weekend, and imagine yourself on Montana’s tropical beaches. Or, you know, get back to work, whichever you prefer.

Three hundred fifty million years ago, a warm shallow sea covered the area of what are now the states of Montana, Idaho, Wyoming and the Dakotas. Actually, the ocean level was so high that most of the western hemisphere was underwater. People who know about such things compare the water that covered Montana to the Gulf of Mexico-warm, shallow, and thick with tiny marine organisms. When these creatures died, their bodies sank into the muddy sea bed. Over time (millions and millions of years) their skeletons compressed and metamorphosed into Madison Limestone-the pale gray rock so common in Montana, Idaho, Wyoming and the Dakotas.

Limestone is an interesting material. On the one hand, it is porous and calcite (the main ingredient in both limestone and Tums) is relatively easy to dissolve, leading to the creation of the spectacular formations of the Lewis and Clark Caverns and the other caverns that dot Southwest Montana. On the other hand, Montana’s dry climate and alkaline soil makes Madison Limestone the most durable rock in Montana. Most of Montana’s mountains feature limestone pinnacles, and most of the cliffs and ridges and most noticeable features (like the dramatic canyon along the Clark Fork, or the Beaverhead formation by Dillon) are Madison Limestone. Limestone’s durability in the Montana climate also means that it has featured in many of the state’s iconic buildings, like the Montana State Capitol.

Tags: geology, intro science, Lewis and Clark Caverns, Dillon, Montana State Capital