I googled your suggestion and found this route, does this look like what you are suggesting? Why the gearing comment? It doesnt look like this gets much over 6%.

Joshua Tree to Keys View - San Bernardino County, CA

If I did this, would probably have family SAG support, so water would be a non-issue. Although I wonder how early cars can get into the park. I'd rather do a loop, I think, if possible. Or maybe just ride through the park.

Thanks for the weekday tip, I could do this on Friday for sure. Which happens to be my birthday so when family asks what I want for my birthday, I can just say "SAG me through Joshua Tree?".