Does anyone know a source of slope maps? I'm looking for a map showing very shallow landscape (<5%). On Google's image search, I found this single map, which is basically what I want, but I'd prefer if there was an online interactive version that I could zoom in, overlay other GIS data onto it if possible, etc.
I could download DEMs, import them into TG, then make a surface color corresponding to the max slope of 5%, and render that out, but that's a lot of work. Plus, it won't give me a standard map projection if I want to overlay Mercator maps of demographic data or county borders onto it in Photoshop.
Elevation does not matter, so valleys or plateaus are fine. I'm not looking for topo maps, as those aren't as instantly readable.
I'm looking for the U.S. southwest, California and Arizona.