Great Post, Slag. Good divisions of eras. But I'm a bit confused on your California geography, but I may be misunderstanding what you're describing. You juxtapose Death Valley and and the Salt Lake Basin; actually Death Valley is about an hour's drive from Mt Whitney, which is part of the southern end of the Sierra Nevada Mountains, the 'magnificent wall of granite' as you aptly describe them. Of course, by wagon in the 19th century that was probably a good three day trek. While, the Sierras join the Cascades in the north, I don't believe they actually join the San Gabriels. BTW, I live in the San Gabriel Mts. about 15 miles nw of downtown Los Angeles (but at low elevation, relatively speaking.)
Thanks for the post.