Joshua Tree National Park: Geology Road Tour

Both of us wish we had retained more of the geology courses we took in college. On the other hand, that was a long time ago, and geology has changed much. "Plate tectonics" was the merest conjecture way back then. Perhaps it's not too late to learn a little more. But I digress.

The kind of formation in Joshua Tree NP that interests us is something we have seen, we think, in a few other places...Brittany, New Zealand, and, mostly, Homestake Pass, near Butte, Montana. Wildly piled and eroded rocks, big rocks, rounded in some dimensions, and not something one can easily explain by glaciation, wind and water, etc. The formations here are something called monzogranite, igneous rock that formed of magma and fractured mostly below the surface. In Joshua Tree NPs' case, the monzogranite formed and eroded, in uplifts, some 15 miles below the surface gneiss, which over some hundreds of millions of years, has mostly eroded away. What one sees in JTNP are humongous rock piles, or insel bergs, island mountains, which, seen from a distance, look like they must be sandstone, but which are really granite, the kind of rough granite favored by rock climbers everywhere. Joshua Tree attracts more than its share of climbers.

Anyhow, we drove the "geology road tour," an 18-mile partly 4WD drive, which, via pamphlet and signage, explains much of the geology of the area and more.

Rock piles at Joshua Tree

Thus

Thus

And thus

What the stuff looks like close up; hard as a rock, too

More piles

Ditto

Ditto

And ditto

Blue gneiss eroding off the monzogranite

Up closer

The road ahead

Shifting into 4WD now, heading across washes and a dry lake

Lots of mining around here in days of old; and target practice
(Ken, note)

The road goes ever on

But we take the one marked "exit"

A bit later, back on the main road, we are exploring the Hall of
Horrors and other rock-climbing areas

Thus

And thus