The Palomar Divide Road (FR 9-S-07)
As of August 2008, the road north from Aguanga may not be publicly accessible due to the number of "No Trespassing" signs that have grown up there like weeds. Instead, the Palomar Divide Road (Cleveland National Forest Road 9-S-07) appears to be the most publically accessible route to Palomar Mountain Summit. This road runs 13 miles to the top. A 4-wheel drive vehicle is probably a good idea.
In the town of Aguanga at the junctions of state routes CA-79 and CA-371, travel east on CA-79 for about 12.5 miles through the town of Holcomb Valley (on the map) or Sunshine Summit (say the signs) to the junction with FR 9-S-07. Keep an eye open as the sign is set back in and it is very easy to drive right past it.
The first mile and a half is typical low semi-desert scrub, mostly open, dusty, etc. The road is bumpy but not too bad overall.
The road is paved from about 1.5 miles to about the 6 mile mark (it is shown on the map, too). Don't get too excited: it's just a layer of asphalt over the road. The road is very narrow, steep and exposed, and you will still likely poke along at 10 m.p.h. My guess is that this section is prone to erosion and it's cheaper to pave it than to come out and regrade it all the time. The pavement ends high up on the ridge near some ruins of an old building. You get your first views of the summit (with lookout) and the nearby observatories.
From the end of the pavement to the 8-mile mark (junction with the Barker Trail), the road is pretty good. For the remaining mileage to the summit the road drops a notch in quality: narrower, a bit more rocky, chewed up, bermed, etc.
We parked at 11.1 miles in a glen of trees, 5,700 feet elevation. I hiked it from there. The road is certainly drivable. If you drive, look for a Y-junction as the road descends (at the 11.2 mile) and go left. This is a short-cut, saving you about a quarter mile and some elevation loss. Stay the course and go left again at the last obvious junction. You'll have to park at the white gate that blocks the final leg to the top.
I always play these roads conservatively. I would not suggest a passenger vehicle up here, since the road past the 8-mile mark is a little more rough, with potential high-centers that could cause trouble for low-set cars.
High clearance is suggested, and 4-wheel drive probably a good idea for some parts. Just go slow and watch the various bends and tricky bits.
Allow about an hour to drive in.
In wet weather the road may be gated shut. Give it a miss if it's raining; the narrow road would be slick and easy to drive off of.
My trip report:
Palomar Divide Road, 8-17-08