In geologic terms, the San Rafael Swell is an anticline: a fold in the Earth’s crust that looks like a dome in cross-section. The Swell formed between 60 and 40 million years ago, when the Rocky Mountains were rising to the east, both uplifted by the same forces deep in the Earth’s mantle. As the top and sides of the dome split and fractured, rainwater found its way into the cracks, eroding them deeper and forming a convoluted network of slot canyons that drain the Swell, some only a few feet wide but hundreds of feet deep.
The eastern side of the Swell, called the San Rafael Reef, is the most dramatically tilted and fractured part of the dome. Made up of steeply tilted layers of erosion-resistant white Navajo sandstone and red Wingate sandstone, these hard rocks have formed into upright fins, cliffs and deep canyons.
I’ve visited the San Rafael Swell a few times and have wriggled through its slot canyons and tested my navigating skills by hiking cross-country into its labyrinth of folds, but I hadn’t yet seen it from on high. And you all know how I love learning about the landscape from altitude! So Dan and I set our sights high: a nine pitch climb to the top of the San Rafael Reef up a route called Death By Chocolate.