Drive up over Cajon Pass to Silverwood Lake and you trade the valley heat for swim, ski, and fishing water, with a campground on the bluff to sleep it off. Fontana has no drive-in campground of its own, so the honest first night is a short run north on I-15 rather than anything in town. The one catch is summer weekends, when the lake gets busy.
Silverwood Lake, over Cajon Pass
The reservoir sits at about 3,300 feet against the San Bernardino foothills, cool enough at night to earn the climb when the valley floor is baking. Boaters get a ski zone on the north arm and no-wake water in the coves, and swimmers get two beaches on the south end, with a paved path across the sand to the high-water line at Cleghorn. From Fontana it's I-15 north through Cajon Pass, then CA-138 east to Cleghorn and Sawpit Canyon Road.
Mesa Campground is the bed, up on the bluff above the water. New Mesa keeps full-hookup RV sites open year round, Old Mesa's non-hookup loop is cheaper but its sites 1 through 65 close for the winter, and both cap trailers at 32 feet. A longer rig has to book elsewhere; California's RV rentals are on the state hub. Book park 716 on ReserveCalifornia up to six months out.
If you'd rather stay close and rough it, Applewhite Campground sits up Lytle Creek off the I-15 Sierra Avenue exit, with the creek running across the road. It has no hookups and no potable water, the paved aprons are narrow, and as of August 2026 there is a fire ban and the picnic area across the street is closed, so bring your own water.
Joshua Tree, east on I-10
When the plan is desert instead of reservoir, Joshua Tree National Park is the run east on I-10, and the Joshua Tree campervan page has where to sleep inside and around it.