This is a fantastic hike passing over some interesting rock formations and joining the Piedra Blanca Creek, which seems always to have water flowing, even in dry years. The trail head is located at the end of Rose Valley Road, at the former Lion campground, which is now a large parking area. A $5 one-day Forest Adventure Pass is required to park here (obtainable from Ranger Stations or sporting goods stores). Drive all the way to the east end of the parking area, where you see restrooms, a large map of the Sespe Wilderness, and signs pointing to the trail. You'll walk east for about half a mile before crossing the Sespe. There's quite a bit of water in the creek now (1/21/2015), but last summer, before the December 2014 rains, it was bone dry. Crossing is easy right now, over stepping stones. In wet years, it can be quite a torrent. Upon crossing, you will soon arrive at a trail sign. A right turn here takes you downstream along the Sespe. (One destination in this direction is Willett Hot Springs, a pleasantly warm, but sulfurous, hot springs around which someone has place a metal tub for your bathing convenience. This is a very long trek though, about 19 miles round-trip.) Turning left at the trail sign puts you on the Gene Marshall trail, and heads toward our destination on this hike, Piedra Blanca camp. On the way, you will encounter another trail junction, where you turn right. If you enjoy scampering over rocks, this is the way to go. There are many interesting formations here. After passing through the rocky area, you eventually join with Piedra Blanca Creek. We stopped at an area that I remembered as the camp from the last time I was here, about 25 years ago, but there is no sign marking it so. It is possible that the designated camp is a little farther along, but this is a very nice place to stop, and we had already walked farther than the mileage indicated on the Forest Service map.
The next camp after Piedra Blanca is Twin Forks, only 0.3 miles distance. If you're up for it, it too is a nice destination, located at a creek junction with many trees. The Gene Marshall trail passes through several other trail camps (Pine Mtn. Lodge, Haddock, Beartrap, Upper Reyes) and ends at Reyes Creek campground, the total distance from the Rose Valley trailhead being about 18 miles. This would be a great overnight (maybe two overnight) backpacking trip.
Tips: Rose Valley is reached from Ojai via highway 33 (14.8 miles from Ojai). After steadily climbing, you'll crest a summit and begin a slight descent. Look for the Rose Valley Road shortly on your right. It's about a 45-minute drive from Ventura to the turn-off for Rose Valley. From there, the road is paved all the way, though a little narrow in places, to the Piedra Blanca trailhead. In summer, it can be very hot on parts of the trail. Bring plenty of water. Best times are winter (avoiding rain/snow storms) and spring.