Box Springs Mountains

The Box Springs is not a large mountain range, but its location, not its size, makes it a fairly prominent feature in inland southern California. It juts up in the middle of the Inland Empire, separating Riverside from Moreno Valley from Loma Linda and Redlands, about halfway between the San Bernardino Mountains, separating suburbia from the desert, to the Santa Ana Mountains, beyond which lies the alternate dimension that is Orange County. It is not a particularly unusual range compositionally, consisting mostly of granite and granodiorite, with some diorite, that was uplifted by faulting. It is a good place to introduce people to igneous rocks in the field (all of the Geo1 classes here go into the Box Springs for one lab), and it has some nice examples of granitic pegmatites and of weathering by lots of wind and not much rain.

The Box Springs also happens to be the backdrop to our campus, marked with a huge concrete yellow C that's a common destination for hikers when the weather is temperate. Considering that the street on which I live goes right up to the base of the mountain, there's really no excuse for why I've only gone up a couple of times. A couple of my friends from the Javanese gamelan ensemble in which I play felt like going hiking today, so we headed up there - only my third time ever.

Today's hike pointed out what I personally think might be the most geologically interesting thing about the Box Springs - the view. Because the range is fairly central, on even a moderately smoggy day (but not a day on which the whole region is on fire), one can see many of the large scale features of the area. The San Jacinto Fault runs through the Box Springs, so looking down the length of the range (and following that same line to the northwest, past the last peak) shows the location of that fault. Looking north from the big concrete C, there's a fantastic view of Mt. Baldy, the highest point in the San Gabriel Mountains. At the base of those mountains, one can see a little bit of alluvial fan patterning before suburbia encroaches on the slope. Looking in this direction, the notch of the Cajon Pass, where the San Andreas Fault pulls the darker San Gabriels past the fainter San Bernardinos, is also clearly visible. From here, looking to the west shows the line of the Santa Ana mountains, with the Elsinore Fault tracing along their base. On the loop of the trail we took that went between two of the peaks, we got an excellent look at the San Bernardinos and their San Andreas straight base from the Cajon Pass to where one of the Box Springs peaks blocked the view. There were some other trails heading down around that peak that we didn't take, but I'd like to go down that way some time, since I can at least hope that the whole straight section until the fault hits the San Gorgonio knot could be seen from up there.

(I'd post photos, except none of them came out terribly well due to distance and encroaching smog. Bah!)

I tried to refrain from going on and on about how awesome I found it to be able to see all these major features in panorama from the middle, since I figured not all ethnomusicologists or composers would find this as exciting as I do. But as soon as one of my friends' attention was pulled in by the shininess of k-spar in a pegmatite, and as soon as she asked me what it was, all bets were off, and I kept pointing things out. The comment that, "I had no idea this stuff could be so interesting," was all the reason to keep talking.