Avoid this one when muddy.
Lower Spring Creek is the better half of the Spring Creek trail for bikes. It dries out earlier than the higher plateau rides.
This ride is shown as a loop, starting at the lower (northern) trailhead, and riding up Dave Wood Rd. to the sourthern trailhead. This gets the climbing out of the way on the road, leaving about 7 miles of fun singletrack descent on the way back.
It can also be ridden as an out and back, riding up the trail, then turning around and descending home. It's definitely rideable in both directions.
Park at the lower (northern) trailhead and climb up Dave Wood Rd. Ride about 7 miles south, and at the Forest Service boundary, take a right on the Spring Creek Rim Road. After about a mile, branching right off the road will be the Spring Creek trail.
The first part of the trail is a doubletrack climb to the edge of Spring Creek Canyon. As you approach the canyon, turn right and parallel it for about 1/2 mile. A 160 degree turn left off of this doubletrack takes you steeply down into the canyon with a loose doubletrack and a number of jumpable berms.
After you reach the canyon bottom, turn right and cross the gate to the Lower Spring Canyon. Here is where the fun singletrack descent starts. There are a few rocky sections and a couple of short steep climbs. Watch out for cactus.
Unfortunately, there is a steep, loose section at the north end that usually requires you to hike your bike up. Once you get back to the canyon rim it is a short jaunt back to the trailhead.