Red Top is #42 on the Sierra Club San Diego Peaks list. It is probably the most difficult day hike on the list (along with Sawtooth Mountains HP). It is part of the small and isolated Sawtooth Mountain range, completely surrounded by other mountains (Laguna Mountains to the west, Inko-Pah Mountains to the south, Tierra Blanca Mountains east and north). In addition, Canebrake Wash and the Inner Pasture separate it like a moat. This makes for a long day hike regardless of how it is approached.
There is no official trailhead, but at least three proven routes. Probably the easiest starting point is from North Indian Canyon Road.
From the north, take highway 78 to S2 (Great Southern Overland Stage Route) and turn south. Continue 29 miles to Indian Gorge Road on the right. This is an unmaintained dirt road that requires 4x4 and high clearance due to soft sand and large rocks. Follow the road a couple of miles until it splits into Indian Canyon Road North/South. Follow the north road (right) another mile or so and choose a place to park off the road. There are no parking spots.
From the south, take Interstate 8 to Imperial Highway near Ocotillo and go north. Imperial Highway turns into Sweeny Pass Road, then S2. Continue about 18 miles to Indian Gorge Road on the left. This is an unmaintained dirt road that requires 4x4 and high clearance due to soft sand and large rocks. Follow the road a couple of miles until it splits into Indian Canyon Road North/South. Follow the north road (right) another mile or so and choose a place to park off the road. There are no parking spots.
The shortest route starts from an unofficial spot of North Indian Canyon Road (see above). Go north over the open desert for 1 mile over the Tierra Blanca pass (about 400' gain), then descend another 1.5 miles to Canebrake Wash. From there, you can head directly for the west ridge and follow it up, or take an old dirt road east for 4 miles to a prominent ascent gully. The gully is the most popular way to ascend. Head up the gully, then northwest toward Red Top. There are no trails, but a faint use trail may be found in places. Route finding is an issue with large boulders, cactus, and thick brush. The brush and route finding get more difficult the higher you go. The final couple of hundred feet is mostly class 3 scrambling. The summit block is class 3 with a friction move onto a small ledge. This route is 16.5 miles round trip, 4238' gain. Red Top is frequently climbed with the Sawtooth Mountains High Point (about 1 mile away). Because of difficult terrain, Sawtooth adds 2-3 hours to the trip.
Other possible starting points:
McCain Valley - Longer route with 2000' of gain on the way back.
Agua Caliente County Park/Moonlight Canyon - Longer route from the east.
Because the Anza-Borrego desert gets very hot in the summer, the best time to climb is fall and winter (October through February), though early spring is also possible.
Camping is allowed in most places in Anza-Borrego without fees. Please check the official web site for requirements.
Anza Borrego State Park: http://www.parks.ca.gov/?page_id=638
Iron Hiker's Trip Report: https://ironhiker.blogspot.com/2018/12/red-top.html
Ben Baumann's Trip Report: http://silverset.net/100-peaks-in-san-diego/197-april-15-2012