Wind-rippled grasses, swaying California poppies, statuesque oak trees, trickling streams, and a 39-acre vernal pool -- it's all there on a sunny spring day at the Santa Rosa Plateau Ecological Reserve. The 8300-acre reserve lies in the fast-growing southeastern corner of Riverside County, but you won't feel as if those people-packed suburbs are nearby.

Follow Interstate 15 north from San Diego into Riverside County, and take the Clinton Keith Road exit in the community of Murrieta. Drive south on Clinton Keith Road, passing the reserve's visitors' center (open weekends) after 5 miles. Keep going, and note the sharp rightward bend at 6 miles where the road's name changes to Tenaja Road. At 0.7 mile past this sharp bend, park your car at the Hidden Valley Trailhead parking area (on both sides of the road). There's a small day-use fee, payable here.

The six-mile looping hike starting from this trailhead will give you a comprehensive look at the reserve's best features. Begin by heading southeast on the Coyote Trail. After 0.5 mile, turn right on the Trans Preserve Trail. Follow it for 1.5 miles over rolling and sometimes wooded terrain, passing through part of the reserve's 3000 acres of remnant native "bunchgrass prairie." Reserve managers have been implementing controlled burns to discourage the growth of nonnative grasses and encourage the recovery of native plants.

The final half mile of the Trans Preserve Trail rises to a plateau called Mesa de Colorado. At the top of this mesa, you turn left on the Vernal Pool Trail and soon visit one of the largest vernal pools in California (39 acres at maximum capacity). The hardpan surface underneath vernal pools is quite impervious to water, so once filled during winter storms, the pools can dry out only by evaporation. Unusual and sometimes unique species of flowering plants have evolved around the perimeter of this and other vernal pools throughout the state.

Continue east on the Vernal Pool Trail, and descend from Mesa de Colorado to the two adobe buildings of the former Santa Rosa Ranch, 3.3 miles from the start. Constructed around 1845, these are Riverside County's oldest standing structures.

After a look at the adobes and a refreshing pause in the shade, make a beeline north on the Lomas Trail. You'll jog briefly right on Monument Road, then go left to stay on the Lomas Trail. At the junction with Tenaja Truck Trail ahead, go straight across toward the looping Oak Tree Trail. It's better to take the left (streamside) branch. Both alternatives give you a close-up look at some of the finest Engelmann oak trees anywhere.

At the far end of the Oak Tree Trail loop, you come to the Trans Preserve Trail. Use it to reach the Coyote Trail, where a right turn and a retracing of earlier steps takes you the final half mile back to Hidden Valley Trailhead.

Note: An incident involving a mountain lion stalking two hikers on one of the reserve's trails resulted in a temporary closure of the reserve earlier this month. That mountain lion has left the scene, but it would be wise to call the reserve before your visit: 909-677-6951.