Overview"Bighorn Mountain" is the high point of the Bighorn Mountains, a small range at the southern edge of Johnson Valley a few miles north of Joshua Tree National Park. It is ostensibly named for the desert bighorn sheep native to the area. Indeed, there is plenty of evidence that, despite heavy use by off roaders, bighorn sheep indeed live there: hoofprints and droppings are everywhere.
The peak lies within the Bighorn Mountain and Whitewater National Recreation Lands area, and is included in BLM's Bighorn Mountain Wilderness area. Although the summit may be reached by 4x4 vehicle (if you're willing to ignore wilderness restrictions), it's worth a visit. The road makes a perfectly good hiking trail, and it provides consistently good views of the Johnson Valley and surrounding mountains.
Due to its desert location, Bighorn Mountain is best visited in the fall, winter and spring. There is no water, and summer temperatures can easily be in the 100's.
Getting ThereGetting to Bighorn Mountain takes a sturdy, high clearance vehicle. There is over 10 miles of sandy, occasionally rocky unmaintained dirt road between the trailhead and the nearest pavement. If you're not confident in your vehicle's ability to get traction in deep sand, don't go, or get a different vehicle.
From the south: Head toward Joshua Tree National Park. When you reach the town of Yucca Valley from either east or west, take highway 247 north (stoplight). About 11-12 miles north of town you will turn left (west) on New Dixie Mine Road. New Dixie starts out as a nice, graded dirt road, but after about a half mile you pass the last residence, and the road goes to pot. The main obstacle is sand, but there are a few rocky spots that require careful navigation. There are many roads branching off New Dixie. In general, continue heading west on what looks like the most well-traveled way.
About 9.2 miles from the pavement take a sharp right turn (Zdon calls this a "triple junction", but it ain't so obvious when you get there) and continue another mile and or two, or however far your vehicle will take you, but in any event no higher than about 5,700', where the wilderness boundary is encountered. There are a couple of forks, which you may or may not notice. Stay left. Park where convenient, and continue on foot (or mountain bike) up the road to the summit. The register is located in a pile of rocks on the northwest end of the summit plateau. Look for an old fence post and a tangle of wire. About 6 miles R/T from the 5,300' level, with ~700 feet of gain.
From the north: From Victorville on I-15, take highway 247 east for many miles until you reach New Dixie Mine road just before the turn-off to the town of Landers. From here follow the directions above.
There a quite a bit more roads in the area than are shown on USGS maps, though the ones you want are represented. A good map and a GPS can help resolve questions as to where you are, and which way to go. Zdon has driving directions, as does the Sierra Club, but it's best to have your own resources.