Eastern Mojave Vegetation View across Wild Horse Canyon  


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  California, San Bernardino County, Mojave National Preserve, Wild Horse Canyon
Photograph taken May 29, 2008.

I have seen some collections made in Wild Horse Canyon, that gave an ecological association of "Joshua tree woodland." However, I don't think I have ever seen Joshua trees in Wild Horse Canyon. I contacted the collector who was quite certain that there were Joshua trees in the area, but that they were not recovering well from the 2005 Hackberry Complex fire. So I went to the location of the collections, as given in geographic coordinates, and searched for Joshua trees. The location is shown in the photograph at left. I searched both sides of the road, across the wash and up on the benches on either side of the wash. I did not find Joshua trees. I did find burned stumps and sprouts of Banana Yucca (Yucca baccata) and Mohave Yucca (Y. schidigera), but not Joshua trees (Y. brevifolia). I'm not saying the Joshua trees aren't there. I'm just saying that I could not find them.

You might wonder, of course, what difference does it make? In my observation, Joshua trees occur on the northwest side of the Mid Hills ridge. They also are found on the ridge line. However, Joshua trees are not found on the southeast side of the Mid Hills ridge, until one reaches the higher elevations of Pinto Valley.

I want to hypothesize that the Mid Hills ridge creates a small orographic precipation increase on the side from which winter storms come, the northwest side. The ridge also casts a small rain shadow on the lee side, the southeast side. The orographic effect and rain shadow are enough to affect Joshua tree distribution in this area. If there are Joshua trees in Wild Horse Canyon, then they provide a counter-example to my hypothesis.

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Date and time this page was prepared: 7/13/2024 8:16:46 AM