Throop Rocks

At first glance, the Throop Memorial Garden looks to be just what it says it is—a lush plot of greenery and water features that offer respite from the sun for turtles, koi, and people alike. But a closer look at the plaques attached to large boulders on the east edge of the tiny campus park reveal that some of the hardscaping also serves as an exhibit of local geological history. Where Throop Hall—Caltech’s first building—once stood proud, rocks representing nearly 2 billion years of the binding of minerals and mineraloids in the San Gabriel Mountains now dot the gently sloped hillside. Grouped according to type and age, the eight different types of rocks that can be found in the garden include 1.7 billion-year-old ancient gray gneisses from Brown Mountain, distinctive pink granite that once underlaid Echo Mountain, and mystery boulders initially found in the Arroyo Seco that, according to the plaque, were “clearly transported there by man,” and whose original sources and ages are unknown.

Photo by Van Urfalian