Who put the stripe in my granite?

The two gods that gave birth to much of the Sierra Nevada were fire and ice: igneous rock (rock formed from the cooling of super-hot magma or lava) and the ice of glaciers. Evidence of both is all around you on the trail.

The magma was first, slowly cooling and solidifying beneath the surface of the earth into the granites that compose so many of the monuments we know (and, in some cases, climb). Then came the ice, in the form of huge glaciers, which moved across them – sometimes polishing the surface to the smoothness matching that granite countertop you have in your kitchen, other times leaving huge erratics (the boulders we see strewn across flat areas randomly, like one-ton runes cast there by giants).

The “domes” (or fractions of domes) that we know so well are the direct result of the granite sometimes yielding to the glacier, and the glacier sometimes yielding to the granite.

At times the geology is smaller and more intimate. Take, for example, the igneous rock dikes you’ll see from time to time along the trail. At first they look almost man-made. After all, straight lines rarely occur naturally. But the strips (like the one you see in the photo, above) were not applied by lunatic road-stripers from the Department of Transportation who got lost in the woods. Instead, these rock dikes were formed in a two-step process.

First, the granite had to harden and split. It turns out the granite hardened better than most rocks because it cooled so slowly, allowing very large crystals to form within it. But even the hardest of rocks can split; there is nothing harder than a diamond and it can be cleaved in two. When that happened a space was formed between.

At some point that space between the two parts was filled with more magma, often of a different composition. In the photo the white strip is made up of rock that is predominantly feldspar. All these eons later it sits right there, a few feet from the trail, ready to tell you a story…if you’re listening.

Good hiking, Ray