Borrego Desert: Clark Valley
See Flora of Clark Valley Area for an area map and the topo map for the Clark Valley Floristic Area of the Borrego Desert. This page gives photographs of the area and additional information on this area.
Clark Valley is a relatively-undisturbed area that probably has some similarities to what Borrego Valley looked like before humans destroyed most of the natural areas there. Although Clark Valley was used for cattle ranching, that is a much less-severe disturbance than farming or bulldozing the land.
In many places of Clark Valley, even just a few miles from S22, you get the sense of being in a natural place that hasn't been changed by humans. Vistas are wide, with no homes, antennae, roads, or mines in sight. The only exceptions are the clusters of tamarisk trees in private land just north of the Lake.
Clark and Borrego Valleys are both "pull-apart" basins, similar to the Salton Trough to the east, and Badwater Basin at Death Valley, which are crustal blocks that have dropped in elevation due to slightly-oblique motion of their neighboring faults. Clark Valley is dropping so quickly that its entire valley drains into Clark Lake.
From many places in the Valley, you can see the Clark Fault, a strand of the San Jacinto Fault, by the fairly sharp area with low elevations on both the northwest and southeast of the Valley. In addition, at the southeastern end of Clark Valley stands Lute Ridge, a strike-slip pressure-ridge fault scarp two miles long and 2100 feet high. Lute Ridge is said to be the largest known fault scarp on the North American continent existing in unconsolidated sediments (Remeika and Lindsay Geology of Anza Borrego, 1992, pp. 47, 102).
Bill Sullivan took the following beautiful picture from about 2000 feet elevation on the ridgeline route to Villager Peak in the Santa Rosa Mountains on the southeastern side of Clark Valley:
See also unlabeled picture and another viewpoint from about 3500 feet elevation (with labels).
View from southeastern portion of Clark dry Lake looking northwest toward Toro Peak:
View from southeastern portion of Clark dry Lake looking northeast to Rabbit and Villager Peaks:
Bill's two pictures were taken from south of Villager Peak, which is beyond the right edge of this photograph.
See also a panorama created by stitching together the above two photographs plus two more, using Autostitch, and the panorama with peaks identified. In the labeled panorama, the elevation profile must be distorted to match the camera view, since the profile was constructed from the actual ridgeline, which is not exactly perpendicular to the camera view. Thus, for example, Rabbit Peak (6623 feet) appears lower than Villager Peak (5756 feet) in the panorama because it is at distance of 7 miles, versus 5 miles for Villager Peak. The distortion to fit the elevation profile to the panorama is exactly as expected. The ridge on the right is very close to the camera, and so gets "spread out" in the panorama. The ridge to the left of Rabbit Peak is farther from the camera, and so gets "condensed".
Clark Valley has presumably suffered less from groundwater extraction than Borrego Valley, even though the first well in the Borrego Valley area was dug here around 1904. Stands of mesquite are dying all around the Borrego Valley since the water table has been lowered below their roots. Unfortunately, humans almost never have any respect for the water needs of the native flora and fauna.
The well was dug by the brothers Fred and Frank Clark, who ran cattle here for 45 years. Lindsay (Anza-Borrego A to Z 2001, p.115) reports that J.L. Kelly described the mesas and foothills surrounding the dry lake as being covered with galleta grass from one to three feet high. The cattle, or water extraction, must have killed most of the grass, since galleta grass is not nearly that abundant here today.
Clark Valley is very deceptive! It seems in many places like one monotonous flat area, with a uniform habitat except for the Dry Lake, and a few patches of mesquite-covered low sand dune areas 1.3 miles north of the dry lake. However, on a six mile roundtrip hike on 9 December 2008, Mike Crouse and I went through six distinct areas! Each of those areas gave us a set of new species not seen before on our trip.
The areas we encountered are labeled on the Google satellite map (our route was the large red triangle), and are:
- the wash right next to our starting point, which had the typical wash species of cheesebush, Hymenoclea salsola; Thurber's sandpaper-plant, Petalonyx thurberi; and catclaw, Acacia greggii, with our only specimen of smoke tree, Psorothamnus spinosus, on the trip.
- the burroweed, Ambrosia dumosa, desert on the first third of our leg outward, which had surprisingly few creosote.
- a very low "sand dune" area, at the only drainage that penetrates this far south, that was covered with dune primrose, Oenothera deltoides, along with some desert dicoria, Dicoria canescens. The dune primrose essentially replaced the burroweed here.
- the area right next to the bajada, where we started encountering a few bajada species such as barrel cactus spilling out into the desert floor.
- the mesquite-stabilized sand dunes, with Phacelia distans under the mesquite.
- a creosote-sand dune area, which also had California croton, Croton californicus; and cattle saltbush, Atriplex polycarpa.
Interestingly, we saw no evidence in the plant species we encountered of the very prominent color change in the satellite map from the white-gray area to the blue-gray area. In contrast, the abrupt boundary at the brownish area just beyond the farthest extent of our route, which is the alluvial fan of the mountains, was very noticeable in the field in all respects.
The change in color from white-gray to blue-gray is apparently due to the source of the rocks on the valley floor, and/or the depositional environment of the streams in the two places. The white-gray rocks are along drainages from upper Clark Valley to the northwest. The blue-gray rocks are from drainages in the local Santa Rosa Mountains to the northeast.
It looks like the main reason for the blue-gray color is the absence of finer, lighter-color sand particles. The streams coming off the alluvial fan may be moving too quickly to deposit their sand here, or they may not contain any sand particles, due to their closeness to the source of the material.
Clark Dry Lake is a very interesting area, similar to Badwater at Death Valley, and fascinating to explore.
Most of the lake bed is devoid of any plants at all. Several different conditions here apparently don't allow plants to become established. First, the surface in many places is fine clay, which swells when wet and cracks when dry. This movement doesn't make many plant roots happy. Second, the soil in most places has extremely high salinity, further stressing any plants that might germinate here, and perhaps even preventing germination of most seeds.
This situation is interesting, since this is an infrequent vernal pool, and has the usual assortment of branchiopods, including representatives of fairy and/or brine shrimp, clam shrimp and tadpole shrimp. So it a vernal pool only for animal life, not plant life.
Instead of the normal vernal pool plant life, it has the saline-tolerant shrub plant species in areas next to the clay / salt pan. Some of those may in fact have gotten started in the clay / salt pan, but then accumulated wind-blown sand to eliminate the clay pan on the surface next to them.
The ground surface in some places is composed of small "ridges and valleys" that probably result from heaving when the ground is wet and the clay particles swell:
There are also interesting remnants of the use of Clark Lake as a gunnery range from about 1941 to 1944 during World War II. The training was with small munitions including 0.30 and 0.50 caliber machine guns, 2.75 inch practice rockets and 1.5 pound practice bombs (Lindsay 2001, p. 115).
They didn't do a very good job of cleaning up after the training, since there are a number of 0.50 caliber bullets and cases littering the ground, along with the clips holding the bullets together in the ammunition belt. See pictures of bullet in ground 1, bullet in ground 2, bullet and case. For comparison, see 0.50"/90 (12.7 mm) M2 Browning Machine Gun.
Mike Crouse and I also found remnants of the practice rockets and/or bombs: picture one; picture two; picture three. I'm not sure what these objects were, but they resemble the "four flip-out fins" on this rocket.
Copyright © 2008 by Tom Chester.
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Updated 17 December 2008.