Geologically speaking, the Trinidad Loop is fairly young, owing its shape to glacial flooding about 13,000 years ago. It's hard to imagine these hills as being shaped in the same process that creates ripples of sand in a riverbed as an entire Z train looks like a model train cutting through a land that could have been formed in a matter of hours. The formation of this hill owes its shape to the region around the present day MRL (now BNSF) 4th Subdivision. Ice dams as high as 2000 feet blocked the mouth of the Clark River in present day Clark Fork, Idaho, building a lake that spanned all the way past Missoula. This process happened many times as the glaciers went back and forth during their retreat. When the dams broke, water would empty out as quickly as a couple days and rip up the landscape of Eastern Washington. Interestingly none of this was known during the construction of the railroads in this region, and the notion that glacial floods could change whole landscapes in days went against the science and establishment of the time.
