On my recent “Winter 2014 SoCal Adventure,” I found myself in a dilemma. Should I pocket an easy $100 and burn some morning daylight by sitting through what should be no more than a one–hour time–share presentation, knowing that pigs would fly before I ever bought into anything? Or, should I just forget the quick cash and head for the hills of nearby Joshua Tree National Park? For a summer seasonal park ranger and barely employed geology adjunct, the decision made itself.
I had spent the previous day wandering around Indio, California. I had perused the kitschy gift shop of one of the many date farms in the area, watched their 1950s film on the romance and sex life of a date, and devoured probably 15,000 calories worth of the yummiest date shake I have ever had the pleasure of devouring. I then proceeded to empty my wallet on groceries in an overpriced food emporium. I figured I might as well attend the presentation to make up for my total lack of pecuniary and caloric self–control. California is a serious chunk of real estate to drive around in, and the extra gas money would come in handy. I knew full well, though, that an 18–minute film about the sex life of a date would be a hard act to follow.
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| Who counted Forty Nine Palms at this oasis? |
During the shortened daylight of the winter solstice, sunset in sunny SoCal comes early, around 4:30pm. By the time I staggered out of the time–share offices and into the December sunshine, it was nearly noon and I needed to get hiking in a bad way. After a fair bit of waffling about where to go, I finally hit upon Forty Nine Palms Canyon. The upside of this mildly strenuous hike was its distance and its draw – a mile and a half one–way to one of the Park’s distinctive fan palm oases. Perfect! The downside of this plan, though, was that the canyon is on the other side of the park from Indio. It would take me over an hour to get there and I would undoubtedly be driving back to the condo in the dark. On the upside, perhaps an owl or two might swoop across my headlights…
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| At the start of Forty Nine Palms trail |
Right out of the gate the trail began to ascend into a jumble of rounded boulders that are so emblematic of Joshua Tree National Park. These have been identified as a type of igneous intrusive (or plutonic) rocks related to granite – granodiorite, monzogranite, diorite – that melted and then slowly cooled and crystallized at least 100 million years ago while still beneath the surface. Closer to the surface, rectangular joints or fractures formed in the plutonic rock. These fractures formed either horizontally (due to the removal of some of the overlying rock by erosion) or vertically at the contact with the cooler adjacent rock mass into which the pluton oozed.
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| Plutonic rocks a-plenty! |
Over the eons, groundwater slowly percolated down into the fractures. With this water moving through, some rock crystals along its path altered to clay while other more resistant crystals were loosened and ultimately carried away by the water. Rectangular shapes became more rounded, even though the rocks were still underground. As the climate changed from wetter to drier, eventually this protective ground cover vanished, exposing these rocks to the ongoing surface weathering and erosion that we see today.
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| Trail steps rise past an intrusion within an intrusion |
It was impossible not to notice the size of the crystals along the trail. They were huge! These lighter–colored feldspar crystals can be up to several inches to a side and nearly perfect rectangles. Enclosed in a matrix of smaller grains, clearly they are not called megacrysts for nothing. It is always fun to come upon them and ponder their origin (although I did not have much time for pondering this afternoon, what with sunset due to overcome the daylight very soon). These larger crystals formed due to their being below ground for a long time, but then something happened, Perhaps the entire plutonic mass moved closer to the surface (but did not erupt as a volcano) and smaller, more fine–grained crystals were able to cool faster. Perhaps the chemical reactions that formed the crystals at different temperatures in the magma went to completion and the necessary elements (the potassium, the sodium, and the calcium, among others) were used up. Perhaps both processes occurred.
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| megacrystic feldspars in a finer-grained matrix |
Considering the fact that I had walked maybe 15 minutes from my car and dusk would be descending sooner than later, I realized there must be no more lollygagging at the megacrysts and I had to get moving. Forty Nine Palms oasis awaited.
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| The sun is dropping behind the mountains at Forty Nine Palms oasis |
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| Fan palms thrive in this canyon due to the spring |
Joshua Tree is peppered with major and minor faults, and it is the fault of these faults that desert oases exist. Movement along a fault creates an area of impermeable rock debris. These debris zones impede the normal flow of groundwater, causing it to move towards the surface along the fault instead. This happens to be the case at Forty Nine Palms oasis, where groundwater has localized as a spring that fosters the growth of the palms. The seeds can be transported by birds or mammals such as coyotes, and were even planted intentionally by American Indians or other settlers. Fan palms (Washingtonia filifera) are the only palms native to the western United States; the origin of date palms (Phoenix dactylifera) is unclear but they were probably first cultivated near Iraq. I for one am ecstatic that someone brought them here and am even now dreaming of that date shake.
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| Forty Nine Palms oasis |
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| Forty Nine Palms? Who counted them? |
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| Schist happens in Forty Nine Palms canyon |
I lollygagged for as long as I could, lost count of how many palms there actually were, took a wrong path on my way out of the oasis, backtracked and found the right route, and soon enough was back at my car with minutes of daylight to spare (but not without stopping momentarily to gaze longingly at a small outcrop of schist along the trail). It would be another 75 minutes of driving in the dark before I got back to my condo but I already had a plan for tomorrow. It would be my last day for hiking in Joshua Tree National Park, and I was determined not to spend half of it sitting through another time–share presentation or driving to and from a trailhead.
