I work in the Barstow area. In July in that area expect daytime temps to exceed 105-110 F, humidity less than 10%, often less than 5%. Exercising hard ie bike riding for many hours in these conditions means you probably cannot physically consume enough water to prevent significant dehydration unless you are very well acclimated. The dangerous part is that because it's dry and you're moving your sweat will evaporate very quickly and you won't feel terribly hot...but you'll lose a tremendous amount of fluid. It's very difficult to drink enough water/fluid at night to replace what you lose during the day.
I suggest that you start riding before the sun comes fully up, ride until 10 am (temps will be 90+ by then), find some shade until 4 or 5 pm (when it might drop below 90 again) then ride until it's too dark to comfortably ride. Or you could ride at night and rest during the day.