This is a photo of Root Glacier joining with Kennicott Glacier (in Wrangell-St Elias National Park). This was the view from our flight from Chitina to McCarthy. Specifically, you see the terminal moraines of these glaciers. It may look like just dirt, but it is actually a mixture of dirt and ice many feet thick.
It boggles my mind to think how glaciers have formed the valleys at places like Yosemite and all over Alaska. Great change often happens at such a slow pace that we barely notice it.