Sandstone Canyon - East Approach Trail is a 7 mile out and back trail located near Borrego Springs, CA and is rated as moderate. The trail is primarily used for hiking and is accessible from November until April.
If you do only one 4wd trail in Anza Borrego, this should be the one. It is an easy drive through a sand wash and a canyon. It's not a challenge to drive but the scenery is fantastic. Because the sand can get soft, I'd recommend 4wd. I've seen 2wd vehicles in there but have also seen plenty getting towed after digging in. So be careful.
I reached Sandstone Canyon via a 12.5 mile drive on Fish Creek Wash. A mile or so in on Fish Creek Wash is the Fish Creek Camp which has a vault toilet and primitive camping sites. Fish Creek Wash goes through Split Mountain which is spectacular to drive through. At about 4.5 miles is the trailhead for the hike to the wind caves. Very cool to see. Great views from the top. Bring lots of water for this hike.
There is a small sign that indicates the start of Sandstone Canyon at about 12.5 miles on Fish Creek. The canyon is only about 7 miles. There are two obstacles on the trail. The first is a large rock which can be passed on either side, depending on your rig. To the right heading in is tight but I had "plenty" of room in a 2013 Jeep. To the left are some small to medium-sized rocks but nothing real challenging. We stopped at the next large obstacle which was impassable the first time we were there. Since, several rigs have been able to get over the huge pile of boulders but I'm still too chicken. We chose to watch others brave it and hiked on foot past the pileup.
The drive up 'til then is to die for. The canyon walls are at least a couple hundred feet high and are so close together that at some points on the trail, you can stick your hands out the windows of the Jeep and touch the walls.
We stopped at the big pileup of rocks and had lunch and walked around.
We see hikers every now and then along the drive and I always wonder how and why anybody could walk that far out but people seem to like it!
One last warning: do NOT drive this wash if it is raining or rain is anywhere near the forecast. It turns into a raging river.
Also, pick up Charles Wells' Guide to Southern CA Backroads if you don't already have it. It's THE book to have.