Roadside Geology Of IdahoFrom the ancient sedimentary formations in the north through the overthrust belt in the southeast, Idaho's rocks are as interesting as rocks come. The authors know these rocks well through their years of research in Idaho, which led to their theory explaining the flood basalts of the Columbia Plateau and the hotspot track of the Snake River Plain as the results of a giant meteorite impact that happened about 17 million years ago. David D. Alt and