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| The small Bear Gulch Reservoir was constructed by the CCC during the Great Depression. It is maintained as wildlife habitat today (especially for the amphibians, which have suffered disastrous declines in recent years). |
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| And yes, I realized I was standing next to poison oak (lower left side of the photo above). |
Continuing our previous blog entry about exploring part of the California Mother Lode, we reach the summit of Table Mountain, near New Melones Reservoir. We had made our way across some grassy meadows and oak woodlands, and then climbed up a steep talus slope through brushy thickets to reach the edge of the summit. We walked into a strange forbidding landscape. The summit of Table Mountain at first looked barren and practically lifeless, but it took only a moment to realize it was full of life, especially on this particularly strange day of rain and storms.
I walked quickly over to the other side of the ridge and looked down on Highway 108 and the Jamestown area, including the mothballed Harvard Gold Mine. The ridge is long (miles long) and winding, and flat. But it is only a few hundred feet wide in most places. Boulders of lava were scattered all across the surface. The 'backwards' theme of these post has the most to do with the strange location of the lava flow at the top of the ridge. I'm going to fully explain that in the next post, but first I wanted to mention something outside my expertise: the biology...
As I wandered across the summit plateau, I realized that something was missing: fields of waving grass. It was striking. In the meadows below, exotic grasses were growing profusely everywhere. Up on top, grass was present, but as can be seen below, it is dominated by other plants; especially small flowers and mosses. Clearly the soils were very thin due to the nature of the lava, but these non-grass plant species were doing just fine, from the looks of things.
From what I could understand from some of the environmental studies of the volcanic tablelands, the exotic grasses have never really established themselves on the plateau the way they have in the pasture lands and meadows below. It's too tough of an environment. Apparently, most of the plants up here are natives.
It is a mostly dry and hot environment for much of the year, but for a few weeks or months, rain fills a number of low areas called vernal swales, which provide a unique growing environment for endemic species. Invasive exotic species cannot tolerate the extreme conditions. The vernal swales are broadly similar to the vernal pools found on the floor of the Central Valley (in the few undeveloped areas), but are more rocky with less clay. I saw quite a few unfamiliar flower species.
As I got closer (to the ground, that is), more and more species of plants appeared. I had to step carefully, ponds were everywhere! Most of the flowers were very small, reminding me of the toy flowers a child might use to decorate the outside of dollhouse. A garden of miniatures....
The colors were vivid, despite the grayness of the skies. Actually, as I looked around the skies were not just gray, but threatening. Rain was falling all around us, and a bitter cold wind was sweeping across the summit plateau. I wasn't quite ready to retreat just yet.
I got on my hands and knees and realized I was looking at an entire ecosystem on the surface of a single boulder (below). It was an incredibly colorful palette of living things, and a wonderful confluence of geology and biology.
I generally don't make a practice of quoting long passages of someone else's work if I can do a decent job of paraphrasing. but I'm not much of a biologist, and I have a feeling some of my biology-loving readers might want some of this info. It was buried deep in an environmental impact report by the Bureau of Reclamation about the Table Mountain flora and vernal swales (found here, starting at page 4-29):"Vernal pools are an ephemeral wetland vegetative community with predominantly low-growing, ephemeral herbs. Germination and early growth occur in winter and early spring, often while plants are submerged, and pools dry out by summer. Flowering is often in bands at the margins of the pools. This community type occurs in shallow depressions, ranging from a few meters to tens of meters in diameter. Characteristic plant species found in vernal pools are Pacific foxtail (Alopecurus saccatus), common blennosperma (Blennosperma nanum), Cleveland’s shooting star (Dodecatheon clevelandii var. patulum), toothed downingia (Downingia cuspidata), spinysepaled button-celery (Eryngium spinosepalum), hedge-hyssop (Gratiola ebracteata), Fremont’s goldfields (Lasthenia fremontii), Douglas’ meadowfoam (Limnanthus douglasii var. rosea), white-headed navarretia (Navarretia leucocephala ssp. leucocephala), adobe popcorn flower(Plagiobothrys acanthocarpus), miniature popcorn flower (Plagiobothrys stipitatus var. micranthus), Sacramento pogogyne (Pogogyne zizyphoroides), Delta woolly marbles(Psilocarphus brivissimus var. multiflorus), greater duckmeat (Spirodela polyrrhiza), and Wildenov’s clover (Trifolium willdenovii) (Stone et al. 1993 in Reclamation 1995). Special status plant species that may grow in the planning area vernal pools include Sacramento orcutt grass (Orcuttia viscida), slender orcutt grass (Orcuttia tenuis), Bogg’s Lake hedge-hyssop(Gratiola hetersepala), and legenere (Legenere limosa).So much of the time I am showing people a place that is new to them. It is always fun to show someone the treasures that exist practically in their own backyards. On this hike, I got that experience of seeing a place for the first time. I loved every moment!
Within the planning area, intermittently-formed pools appear after rainfall or snowmelt on top of Table Mountain between 1,200 feet in elevation in the south and 2,600 feet in the north. Although these pools share some of the characteristics of some vernal pools in the Central Valley, they are not true vernal pools in that they do not have a clay underlayer that prevents percolation. Instead, they form in swales in the rocky surface of Table Mountain. The soil is poorly drained and the parent material on Table Mountain is a Pliocene lava flow (andesite). Intermittent pools occur on Table Mountain in seasonally wet to saturated rocky meadows that have slight soil development (Evens et al. 2004). They are interspersed within the annual grassland (Reclamation 2006b). Intermittent pools at Table Mountain do not support the range of species found in vernal pools in the Central Valley, possibly due to differences in substrate(primarily shallow, rocky substrate versus clay substrate in valley vernal pools). Although vernal pool habitats are very delicate and easily disturbed in general, this is even more pronounced on Table Mountain where soils are poor, shallow, and loose.
To date, vernal pools have resisted invasion by exotic plant species, probably due to their ephemeral nature (USACE 1997). However, the scientific community is concerned that exotic plants may colonize vernal pool communities, possibly displacing the highly specialized native vernal pool species (USACE 1997). Despite these concerns, there is no supporting evidence that this change is occurring in vernal swales found on Table Mountain (USACE 1997).
Another day in the field...today it was our Geology Club. It's not enough that I make my students work hard in the classroom and lab, and drag them on field trip courses. The club members raised the funds to go out on their own and see something new and different. Once again the students led the teacher; I even rode in the back of the van! Yup, backwards day it was, in many different senses.
The trail to the summit starts at the end of Shell Road off of Rawhide Flat Road near the gold rush town of Columbia. "Summit" is not the best term though because Table Mountain is not a single peak at all. It is a flat-topped ridge that winds for many miles through the Sierra foothills. It is composed of a basalt-like volcanic rock called latite, and the lava flow displays some interesting columnar jointing in places (below). The flow is 9 or 10 million years old. How did it get to the top of the ridge? That question will be dealt with at a later time.
The trail crosses gently sloping meadows and oak woodlands for a mile, and then turns and climbs steeply for a half mile to the summit ridge. The ecosystem changes drastically as the trail climbs the north-facing slope. The path is shaded by numerous trees and shrubs, with some unexpected species for a region that regularly reaches 100 degrees in the summertime.
It's a thicket, really, and I'm glad we had a trail to follow instead of bushwacking. The poison oak would have been a real problem! In the picture below one can see the edge of the barren summit ridge.
We passed a glen full of ferns opening up for the first time among the brown husks of last year's crop.
The slope we were climbing was composed of large fallen boulders from the lava flow, a feature called a talus slope. The openings between the boulders can extend hundreds of feet into the slope, and cool moist air will seep out of the slopes all year long. Mosses cover the boulders.
I hope my flower-loving friends will identify the flower for me...I haven't noticed this species before (mind you, I'm a geologist, and flowers are as much a mystery to me as minerals are to botanists). It was fairly common and obvious on the shaded slopes.
We were nearly to the top, and had a close up view of yet another series of small ephemeral waterfalls. A few more switchbacks and we would reach the summit, the "top" of Table Mountain. Our backwards story will continue in the next post!
