DryStoneGarden

Posts Tagged ‘basalt’

The Devil’s Postpile and Patio

Devil's Postpile National Monument

Probably the most striking geological feature on the eastside, an area full of geological features, is the Devil’s Postpile, one of the world’s best examples of columnar basalt. Columnar basalt is one of those natural elements that looks unnaturally geometric. It forms when it lava cools very, very slowly and evenly. The lava starts to contract and then crack, and because it cools so evenly the cracks form into hexagons, the most stable and efficient shape. As the Park Service page about the formation of the Postpile explains, “a hexagonal system provides the greatest relief with the fewest cracks.” (Bees use the same hexagonal system in their honeycombs because it forms a matrix with the most storage space for the least amount of wall.) Devil’s Postpile isn’t the only place where this has happened — the Wikipedia entry has links to many other columnar basalt cliffs, and pieces of columnar basalt regularly show up at stoneyards in the Bay Area, probably from quarries in China –but the columns at the Devil’s Postpile are especially long and regular.

The Devil's Talus

The base of the cliff has the world’s coolest talus in my opinion. My crew was so well trained/indoctrinated that their first comment was how great these pieces would be for making steps. The park service doesn’t let you climb on the talus, let alone build with it.

The Devil's Patio

Possibly the best part is that a glaciar carved off the top and made a natural patio.

The Devil's Paver Pattern

It’s uncanny how much they look like rough-cut natural stone pavers. The park service says that 55% have 6 sides, 37% have 5, 5% have 7, and the rest have fewer. That’s a high percentage of hexagons compared to other sites in the world. One of the reasons hexagons are so stable is that three joints come together at every vertex, making for a nice oblique 120 degree angle.