Modern humans came frome the Ethiopian plateau right? So low of 75F high of 80F sort of thing. High altitude equatorial. Bogotá is similar but cooler. As is Quitó. Much of coastal Europe and west coast North America is a decent approximate.
Coastal Europe has considerable variation and the west coast of North America even more so, but what is of more relevance to the snowpack issue is that most of the lower Colorado basin is quite unlike what humanity's home was like prior to our global spread.
