The Arizona Geological Survey has a great looking site with some good information. They have a publication list that can either be downloaded or ordered and are making pdf versions of their recent publications available online.
I was going to note that there was no download-able data available until Google told me that they in fact had a WMS/WFS available online. The WMS is a great looking map, I have not gotten the WFS to work, however–probably more due to my abilities than the service.
They are also temporarily hosting a surficial geology map of Clark County, Nevada.