Volcanic Violence and California's Most Endangered Habitat: The Vernal Pool Prairie

The green hills of California's prairie barely conceal a horrific violent past. Around 20-23 million years ago, huge volcanic eruptions shook the western part of North America. Ash (pulverized volcanic rock) blasted into the atmosphere in unimaginable volumes, 100 cubic miles or more. Some of the ash was driven into the upper atmosphere, to be spread around the world with the wind currents, but much of it settled in layers that covered tens of thousands of square miles. Living things would have been buried at best, incinerated at worst. Any one of these events would have been a catastrophe. But there were many of them.

Some of the ash clouds rolled off of highlands that once existed in central Nevada and flowed west into California and down the western slopes of the slowly rising Sierra Nevada. These ash deposits are called the Valley Springs formation, and this rock still influences life in the present day.

The ash eruptions subsided, but new volcanoes developed at closer quarters, near or just east of the present-day crest of the Sierra Nevada. An occasional lava flow reached the lower foothills of the Sierra, but more often, it was a volcanic mudflow, or lahar, that came to inundate the landscape. The rocks today are called the Mehrten formation. Numerous animals lived on the resulting river floodplains and lakes, include tremendous six-foot long salmon (with "tusks"), and tortoises the size of their Galapagos cousins. Mastodons, horses and camels wandered the plains, chased by fearful carnivores, including the ancestors to the Sabertooth cat.

The geologic violence subsided, and erosion has subsequently smoothed off the hard edges of the volcanic rocks. In the semiarid climate, it is mostly grass and annuals that grow here, although the occasional oak survives in the barren landscape. The volcanic rocks contributed to the unique habitat that exists here today, providing through the weathering process copious amounts of clay.

Most of the minerals in ash will decay over time into one of the clay minerals. Soils that develop at the surface tend to be clay-rich, or clay may be present just below the surface, forming an impermeable barrier that prevents water from percolating into the ground. Because wind can blow out hollows, and because clay-rich layers can differentially settle, small pools of water may remain after major winter rainstorms. Because the water can't percolate, it doesn't disappear until it evaporates. The resulting ponds are called vernal pools. The pools are one of our more unique and unusual habitats in California.

A large number of species of plants and animals have evolved to survive in this environment that swings wildly from wet to dry within a period of weeks, and many of the species are endemic to the state. Colorful wildflowers bloom quickly in the drying rings of the "shores" of the little ponds, growing and setting seed before the water has completely dried up. The seeds can repose in the soil for years at time when drought dominates the landscape. Frogs and other amphibians may burrow into the soil and estivate (remain inert) for months on end, waiting for the rains to return.

We spent a delightful afternoon out on the prairie last weekend. It's not too hard because our village lies on the edge of the grasslands. We traveled Willms Road south of Knights Ferry near Highway 108. The spring flowers were just beginning to make an appearance following a warm dry February. There had been fears that this was the end of our rainy season, but a number of vigorous storms are on tap for the next two weeks, so the pools may be filling again for awhile.

Many birds call the prairie home. We felt especially lucky to see a pair of Great Horned Owls in a hollow along an ephemeral creek. The Valley Springs formation is soft and easy to excavate, but the holes are architecturally sound.

A Savannah Sparrow favored me with a pose on a fence next to the road. It was the first time I've had a chance to photograph one.

It was also the first time that I captured a Horned Lark. I thought at first that it was a Western Meadowlark, but I realized the markings were all wrong.

The Meadowlarks were certainly out and about, though. We could hear them all along our drive. At this time of year, they're looking for mates, and aren't at all bashful.

It was a beautiful afternoon in a serene "wilderness" (these are really private ranchlands), but we were also chastened by the sight of thousands of acres of new almond orchards that have been planted just to the west. The water for the trees is coming from irreplaceable groundwater aquifers, and when they have been sucked dry, the almonds will die away. In the meantime, hundreds if vernal pools will have been destroyed.

The Other California: The Wetlands of the San Joaquin Valley, Actually Wet.

It's been a miserable year, one of the worst on record. For the last year much of California, including my home in the Great Valley, has received an amount of rain more appropriate to Death Valley than to one of the most fertile agricultural regions on the planet. It's been dry and dusty, and the farms in the valley have been surviving off of storage in the irrigation reservoirs, but after three dry years in a row, the reservoirs are on empty.

A Black-necked Stilt

In a valley where farming is king and 95% of the landscape is totally devoted to agricultural development, wildlife concerns take a back seat, especially when water runs short. The valley once hosted millions and millions of migratory birds, but during the development of the farmlands, lakes and marshes were drained and plowed, and what few birds persisted got themselves driven off or shot for consuming crops when natural forage was no longer available.

No, it's not drunk, and it's not falling over. A split second later it was airborne.

It would be nice to think that wildlife refuges were established to stabilize and preserve the original environment of the valley, but in some cases the motives were less noble: some, like the Merced National Wildlife Refuge where we visited yesterday, were designed to distract the birds from nearby farmlands where they were causing crop damage. And of course many refuges were designed to make it easier to "hunt" and shoot the birds. Whatever the original motive, their form and function has evolved. As we have come to understand the intricate nature of the migratory bird ecosystem, management of the refuges has begun to promote a stable winter home for numerous species. In some cases they have become spectacularly successful: the Merced Refuge protects 60,000 geese and 20,000 Sandhill Cranes. The refuges are managed as a complex ecosystem, with protection extended to the many other birds, mammals, reptiles, amphibians, fish and invertebrates.

A Black-necked Stilt and a Killdeer forage on the refuge road.

Our previous visits to the refuges (which we pretty much discovered only this year after living around here for a quarter of a century) have been dry times. Some of the fields were flooded but so little water was available. The drought has not broken, but we've finally received some rain, and on Sunday we paid a visit during a rainstorm. The birds seemed pleased, and the noise was almost deafening at times. It was delightful.

The Black-necked Stilts (Himantopus mexicanus) were especially common, and cooperated nicely with our efforts to get pictures, so they are the stars of today's post. "Stilt" is an appropriate enough name; their legs are ridiculously long, allowing them to wade in deeper water than some other birds.

There is only one Ibis in the American West, the White-faced Ibis (Plegadis chihi). We saw it for the first time on our last trip here, and were pleased to see it again. According to some of my guides, the bird is in decline California, primarily because of the need for large marsh areas for breeding. Those have been sorely lacking in these dry years.

They have one of the stranger looking beaks I've seen. They are obviously good for foraging deep in the mud.

Their feathers have a beautiful iridescence (that was not real obvious on this cloudy day).

The edge of the refuge include a few trees, still lacking their leaves. We were watching for raptors, but were thrilled to see a huge Great Horned Owl (Bubo virginianus) staring at us. Actually the stare was mildly disconcerting. The curve of their brows suggests malevolence, even though none presumably exists (I hope; given that birds are the only remaining dinosaurs in the world, I shiver to think of that stare coming from a creature fifteen feet tall).

I saw a fencepost off in the distance, but realized after a moment that it was actually a Great Blue Heron (Ardea herodias) standing very still. Another bird who cooperated nicely as we snapped a few pictures.

It is such an elegant looking bird!

We couldn't get very close to the vast flocks of Ross' Geese, Snow Geese and Sandhill Cranes, but we could see thousands of them off in the distance. The picture below is just part of the main grouping of Sandhill Cranes. The managers grow several hundred acres of corn on the refuge to feed the birds and give them full stomachs for the long flight north to their breeding grounds.

We stayed until the sun disappeared below the horizon in a beautiful sunset. This is the Great Valley at its best; I have been guilty of thinking of my home grounds as boring, bereft of geological interest and lacking much of anything resembling a natural environment that recalls the days following the last ice ages when wooly mammoths and dire wolves roamed the prairies, along with horses, camels, elk, bison, antelope, and saber-tooth cats. But here in the setting sun, with the cacophony of hundreds of thousands of birds, I felt a sense of how it once was before we "improved" the land.

The western sky was graced with a beautiful thin crescent moon.

The "Other California" is my long-neglected blog series on the places in my beautiful state that are often missed  by travelers from outside the region, especially those that tell a geological story. Toyota stole my idea, actually. I've never seen a tour bus full of foreign tourists stop at any of these refuges, but I imagine the sight of tens of thousands of geese soaring into the sky would be a sight that would impress any California visitor. And in the American West, the story of such a flat place, full of wetlands and marshes, is truly unusual, considering the geological violence that has occurred throughout the region, raising vast mountain ranges and high plateaus. The diversity of our landscapes, and the wide diversity of our native species is truly stunning.

Note: The San Joaquin Valley noted in the title is the name given the southern half of the Great Valley, from about Stockton to Bakersfield.