Greatcats and Jim, There are a ton of trails around Yuma, the mountain ones are particularly popular, the views are incredible. Of course, any oasis is great for wildlife and bird viewing, and the Yuma area has its share of those, too. If Skim times it right, the wildflowers will be in bloom and some people are saying this will be a good year because of the recent rains.
Skim, We usually did our desert hiking in fall and spring, not the middle of summer, although as a teenager I did my share of backpacking in Death Valley in July because that is when the place is (or used to be) empty ... but I knew the area really well back then. Be sure you talk to some locals when planning your trip.
If a motel won't work with you, talk to the ranger wherever you are planning to go, they may be able to hold your stuff. Visitor center or chamber of commerce people can also be accommodating. Maybe you can find a local on Craigs List even.
If you can get out there, Martha's Gardens has the best date shakes in the southwest, they are very generous with fresh (not dried) pieces.