Like the Snake River I posted last week, today I've got another example of a river happily braiding through a wide valley (this time probably glacial, not structural) only to meet an obstacle in the form of topography. I'm looking at the Lamar River on the northeast entrance road to Yellowstone National Park. We're north of the volcanic plateau here and just west of the Absaroka Range, so I think the geology is typical Cordilleran stuff.

One of the things that fascinates me about this example is how short (and steep) the gorge section is (< 3 km, ~100 m elevation drop). Is it a relict of the glacial influence on valley formation? Or is there something structural going on (the Yellowstone geologic map indicates a fault in about the right area)? Food for thought and an excuse to do some field reconnaissance someday maybe. Or you can go there now in Flash Earth.

Images below are a mixture of Google Earth, Flash Earth, and ground photos from my personal collection.