A vernal pool is a temporary wetland that fills with water during
the rainy season and dries down in the spring. It remains dry for
six to eight months awaiting the next winter rains. The plants
and animals that are adapted to survive these annual extremes of
flood and drought create a changing mosaic of life throughout the
three phases of a vernal pool: wet, flowering and dry.
Millions of years of geology and evolution have created the
spectacular vernal pools at Sacramento County’s Mather Field.
These are exceptional examples of a rare wetland ecosystem that
is unique to California. Visitors can experience this piece of
California’s natural history, just 20 minutes from downtown
While the vernal pools at Mather Field range from 50,000 to 200,000 years old, the soils under them began forming more than two million years ago. Dissolved minerals slowly moved down through the soil, eventually forming a hardpan layer. This hardpan lies a few inches to a few feet below the soil surface.
Although most vernal pool animals are small, their complex food
webs sustain many larger species of birds, mammals, amphibians
and reptiles. Most of the critters in vernal pools are native to
California and many survive only in vernal pools. We know little
about them and less than half have been named.
Over 200 plant species grow in vernal pools and the surrounding
prairie. Half of these are rarely found outside this unique
habitat. A single pool typically supports only 15 to 20 species
in an unpredictable array of combinations. In that way, vernal
pools are a lot like snowflakes – botanically speaking, no two
For 2 billion years, bacteria were the only creatures on Earth.
Long before the dinosaurs, a special type of bacteria slowly
increased the level of oxygen in the Earth’s air to 20 percent.
Without this oxygen other plants and animals could not have
evolved, including us.