One of the largest vernal pools in California (39 acres at maximum capacity) lies in a shallow depression atop near-flat Mesa de Colorado, in southwest Riverside County’s Santa Rosa Plateau Ecological Reserve. Small vernal pools were, before the spread of cities and suburbs, common in coastal San Diego County. Here, not far from the sprawling cities of Temecula and Murrieta, you can see a vernal pool that is both undisturbed and framed by a backdrop of gorgeous natural scenery. That scenery promises to be engaging to the senses for at least the next three months because of the generous amount of rainfall that fell in the area late last year.

To get to the pool’s access point, head north on Interstate 15 into Riverside County. Beyond Temecula, stay left on I-15 as you approach the I-15/I-215 split. Proceed about five miles farther to the Clinton Keith Road exit in Murrieta. Go south on Clinton Keith Road five miles to the Santa Rosa Plateau visitor center, on the left, worth a visit if you have never been to the reserve. You can pay a small fee for day-use parking here or else farther up the road at the Vernal Pool Trailhead. To reach that trailhead, continue heading south on Clinton Keith Road and make no turns off of the main road as the route changes its name to Tenaja Road and finally Via Volcano. The large parking lot for the Vernal Pool Trail is open from sunrise to sunset daily.

Out of your car now, walk due east on the wide, nearly flat Vernal Pool Trail. On winter and spring weekends, this is far and away the most popular trail within the reserve. You and your kids are welcome, but pets and mountain bikes are not. Travel east just 0.6 mile to reach the north side of the large pool, where a boardwalk allows you to approach the pool’s “shoreline.”

The hard-pan surface underneath vernal pools is generally impervious to water, so once filled during winter storms, the pools dry only by evaporation. Unusual and sometimes unique species of flowering plants have evolved around the perimeter of many vernal pools, including this one. As the watery perimeter contracts during the steadily lengthening and warming days of the spring season, successive waves of annual wildflowers bloom along the pool’s moist margin. By July or August, after weeks or months of drought, there’s nothing to be seen but a desiccated depression, its barren surface glaring in the hot sun.

The large pool is also a home for fairy shrimp of several species, and for the spadefoot toad, whose egg clusters may be quite conspicuous.

Vernal Pool Trail
Discover one of California’s largest vernal pools at its fullest phase.
Distance from downtown San Diego: 72 miles
Hiking length: 1.2 miles round trip
Difficulty: Easy