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Sure, you can drive the 370 miles involved in this loop in a day, and maybe even have a couple of hours to enjoy some short excursions. But many of the miles involved will be on two lane roads and particularly those between Palm Springs and Borrego Springs will be slow going through the mountains. What you should lop off is entirely up to you, but I would lop off something!

I've never heard of Atwest. That doesn't mean they're no good. They may be trying to fill a niche that is under-served by the major rental companies. You might start with an inquiry to the Los Angeles Better Business Bureau to wee if they're a member and/or have any unresolved complaints, but this is something you're in a better position to check out than we are.

AZBuck