Vernal Pools Across California Hit Peak Season, Showcasing Rare Wildlife and Wildflowers

Each spring, when winter rains settle on the land, California’s verdant grasslands hide something in plain sight: vernal pools. For a few, brief months, these stealthy pools of water hide beneath the vegetation.

Vernal pools don’t stand out and command attention, but if you look close enough this spring, you will be rewarded with one of the most vibrant and colorful nature’s displays.

Throughout the state, vernal pools are their peak this time of the year.

What Are Vernal Pools?

Vernal pools are a temporary, seasonal wetland, and one of the most ecologically significant and distinctive areas in California, according to the California Department of Fish and Wildlife (CDFW).

Vernal pools are depressions in areas where a hard underground layer prohibits rainwater from seeping into the subsoils. Rainwater fills these depressions in the winter and spring months, where the water collects and remains.

The water eventually evaporates and dries off by summer and fall.

While these pools usually occur in Mediterranean climates globally, the diversity of native flora and fauna found in California’s vernal pools are quite unique, according to the CDFW.

In California, vernal pools range in size from small puddles to shallow seasonal lakes and appear in relatively flat or gently sloping grasslands in over 30 counties across 17 regions, according to the California Department of Water Resources (DWR).

Vernal pools are often connected by small drainage conduits, called swales. These conduits can form vast, interconnected complexes.

Importance of Vernal Pools in California

On a recent spring morning in southeast Sacramento County, DWR Senior Environmental Scientist Clay DeLong offered a look at a vernal pool habitat at the Mather Regional Park, which he said was a “unique grasslands system.”

With more than 10 years worth of experience of working in and around vernal pools in Central and Northern California, DeLong is a passionate advocate of their value to the ecosystem.

“Because of the biodiversity and their relative scarcity, vernal pools are also home to a wide variety of rare endemic plants and animals,” DeLong said.

Most of the flora and fauna found at the vernal pools are special status species of regulatory significance to many of DWR’s projects, he said.

Viweing vernal pools as a botanist, he explained that vernal pools, particularly those in the undisturbed landscapes, house several varieties of wildflowers in the spring.

In addition to wildflowers, vernal pools are home to plants, insects, amphibians, reptiles, birds, and mammals, with the isolated nature of the pools hiding them from invasive species.

Declining Number of Vernal Pools

California was once blanketed by more than 6,000 square miles of vernal pool landscape, before large-scale settlement by European Americans in the 18th and 19h centuries, according to the DWR.

The rapid pace of urban and agricultural development resulted in vernal pool acreage shrinking by as much as 95%, depending on the location.

Recent studies suggest that more than 13% of the remaining vernal pool habitat in the Central Valley (137,100 acres) was lost between the 1976 to 1995 baseline conditions and 2005, according to the CDFW.

Efforts are being made to protect the remaining vernal pools, as their disappearance also leads to the loss of rare animal and plant species, according to the U.S. Environmental Protection Agency.