On my recent journey, I stopped in at the Barstow Superchargers. For folks from Northern California, you will have to go a mile or two out of your way SE on I15 if you are coming from highway 58 and heading east.
The Tesla web site has it listed at:
I15 Exit 178
Country Inn and Suites
Although it is technically in the Chili’s parking lot and not particularly visible.
There were four physical charging stations when I stopped by, but one looked out of service. I saw no Model S cars around.