Vernal Pools at Vasco Caves

We eat our lunch on a sandstone outcropping. A pair of orange-crowned warblers appears and disappears in the bushes. A rock wren chirrs behind us. Then the ranger gathers the group and leads us to where pools, ranging from the size of a sink to a large hot tub, dot the rock.

We bend over the murky water of a pool. Mysterious small shapes move. Some resolve into black tadpoles (sierra chorus frogs), others into water boatmen (small bugs that look like rowboats with pairs of oars). Then we spot one of the creatures we've come to look for: the nymph of a California tiger salamander. The tiger salamander is poorly named- the adult is black with bright yellow spots. The nymph is semi-translucent, dappled green and brown, tadpole-shaped, with an extravagant fringe of gills.

We are also looking for vernal pool fairy shrimp; at first we see none, but later I spot one scrumping along the edge of an algae mat in one of the smallest pools. It is about a centimeter-long, gray, with a row of rippling legs. Eventually, the group finds many more fairy shrimp.

These pools fill with the winter rains, and last only a few months. Here on the east side of the coast range, spring turns hot and dry quickly most years. Fairy shrimp hatch from cysts when they are in cool water. The shrimp eat algae, mate, lay new cysts and die before the pools warm up. A fairy shrimp cyst is incredibly tough: it can survive years of drought. A cyst may hatch one year after it is laid or decades later. Tiger salamanders also use the pools to reproduce. Adults spend the dry season estivating in ground squirrel burrows, then migrate up to the pools during the wet season. They lay eggs, which hatch and become the nymphs we saw. The salamanders and their nymphs eat fairy shrimp. The shrimp thrive in pools that are hard for many salamanders to reach.

The pools, and these rare shrimp and salamanders, are protected in Vasco Caves Regional Preserve. You can only visit the park on a guided tour, a measure to protect these species, and also to protect the sacred Native sites in the park. The sandstone outcroppings and the shallow caves scooped from their sides have been sacred to the local Muwekma Ohlone, Bay Miwok, Chochenyo, and Delta Yokuts* people for hundreds and probably thousands of years. There are petroglyphs made in ceremonies in several of the caves. As we entered the park, we saw a pair of prairie falcons fly from a cliff to the top of an oak. Later, the ranger showed us a petroglyph that likely shows Wek-Wek (prairie falcon) and the myth of his death. Up until people were created, death lasted only four days. Coyote decided that with the arrival of people, death would need to become permanent to avoid overcrowding. We-Wek's was the first permanent death.

We step from one vernal pool to another, peering to glimpse the teeming, tiny lives. Bright yellow flowers and vibrant green leaves carpet the low areas between the pools. In a few weeks, the rains will stop and the pools will dry out. The tiger salamander nymphs will have grown to their black and yellow glory, and buried themselves underground.  The only fairy shrimp will be potential shrimp in time-capsule cysts. The top of the sandstone will be sun-blasted and bare.

Each individual's death is permanent. Our time in the pool is brilliant green and brief. New lives begin with the cool rains.

LINKS
Vasco Caves Regional Preserve
Muwekma Ohlone Tribe
California tiger salamander information from the Pacific Forest Trust
Vernal pool fairy shrimp information from Sacramento Splash
Prairie falcon information from the Cornell Lab of Ornithology

*These names may describe overlapping cultures and/or more than one of these names may describe the same group. This list is likely not exhaustive.