A Fieldtrip to Jepson Prairie

This past weekend, I finally visited the vernal pools at Jepson Prairie Preserve for the first time! I went on one of the docent-led tours, which means I had the chance to see some amazing “scooped” crustaceans, insects, and amphibians, and I was also able to experience the beautiful wildflowers off the path and up close in the field.

Jepson Prairie is located in Dixon about 15 miles south of I-80. There are several different types of vernal pools found throughout California, but the ones at this site are claypan vernal pools, which form when there is an impermeable clay layer close to the surface of the ground that causes rainwater to collect in low areas. These seasonal water bodies drain slowly and play host to a set of very complex and unique ecological relationships. Unfortunately, around 90% of California’s vernal pools have been destroyed, mostly due to agriculture and urban development. Apparently, the land that is now the Jepson Prairie Preserve was probably spared because the soil is particularly alkaline, so it wasn’t seen as useful for anything other than grazing. A side note—according to some of the research and observations by vernal pool experts, carefully timed livestock grazing can be beneficial for vernal pool plant communities because it keeps the non-native annual grasses at bay and gives the native forbs a chance to emerge. Interestingly, I think I saw this in action on my drive down at a nearby cattle grazing pasture, which was completely carpeted with Goldfields as far as my eyes could see.

Anyway, I digress. A really interesting feature of Jepson Prairie is Olcott Lake, which in fact is a gigantic vernal pool! Despite its large footprint, it is very shallow and only made up of rainwater (there are no inlets or outlets), so all the water will be gone by the middle of summer. Thanks to this “playa” pool, the docents were able to collect examples of different aquatic species for us to observe. The Conservancy and Vernal Pool Fairy Shrimps were gone for the season, but we did see the endangered Vernal Pool Tadpole Shrimp and a California Tiger Salamander larva, among some other amazing creatures.

*Olcott “Lake” is a giant vernal pool! By mid-summer it will be gone…*

After the watery part of our tour, we wandered around the wildflower areas. Even though the vegetation is so lush and colorful, it was interesting to note how hard the clay ground felt underfoot. I can see why there aren’t really any plants taller than the grasses, except for some of the human-planted windbreak eucalyptus in the distance. It took a while for my eye to find things and appreciate the close-up details, but by the end I was hunched over and wishing I’d brought my hand lens… One thing I enjoyed observing was how the plants arrange themselves according to elevation, even if it’s only a couple feet of difference. For instance, I would see Yarrow and Purple Needlegrass on the more mounded areas, while Goldfields and Downingia stuck to the lower areas. Speaking of, my favorite plant sighting from the tour was Downingia—I can’t believe I hadn’t heard of it before! There are several different species at Jepson Prairie, each with different coloration patterns.

The docent tours run through Mother’s Day weekend, so if you haven’t been yet you still have a chance! All the docents were so kind and knowledgeable—a huge shoutout to them for sharing their time and expertise…

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A Fieldtrip to Jepson Prairie

Visiting the University & Jepson Herbaria

Spring in the Grassland Garden

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