Ventana Natural Arch

Useful Information

Location: Co Rd 35C, Del Norte, CO 81132.
(37.811924, -106.376412)
Open: no restrictions.
Fee: free.
Classification: GeologyNatural Bridge
Light: n/a
Guided tours: self guided
Photography: allowed
Accessibility: no
Address: Ventana Natural Arch, Del Norte, CO 81132, Tel: +1-719-852-5941.
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The Ventana Natural Arch, or La Ventana Arch in Colorado is also known as La Garita Natural Arch. In the U.S.A. many huge arches exist, but most of them are a result of the erosion of layers of sandstone with different hardness. Often the arid areas have erosion based on wind transporting sand, and on regular daily temperature changes between freezing tempertures in the night and hot days. The temperature changes cause stress in the surfaces of rocks, small amounts of humidity in cracks freeze in the night, the ice expands and the rock crumbles. Such arches exist all over the world, but what seems so normal here, is rather exceptional in other countries.

However, this arch is located inside a lava dike, which is quite exceptional everywhere. There are a lot of steps required to form such an arch. First there is rock, which is sedimentary and thus softer than basaltic rock. Then there is tectonic movement, which creates a crack opening. Magma from below flows into the crack and fills it, becomes hard and thus forms a vertical layer of hard basalt. Then the surrounding sedimentary rock, which is softer, erodes and the basalt forms a vertical wall. And finally erosion of the wall forms a huge opening, an arch, in this wall.

The magma intrusion is lava from the Summer Coon volcanic complex, and about 30 Ma old. The dike forms a series of wall segments, which is 4.1 km long and runs almost north-south. The arch is in the southernmost segment, which is 1.2 km long, about 280 m from the southern end. Located about 18 km northwest of Del Norte, Colorado, it is reached on Forest Service Road 35C. The gravel roads crisscross the hills and connect some small farms and several quite interesting geotopes. A high-clearance vehicle is advisable but not required. From the trailhead at the end of road 35C, it's a short hike to the arch, the trail is only 100 m long but quite rough. The arch is difficult to see from any direction except directly in front of or behind it. But from the trailhead it is hard to miss.

The arch is a sacred site for the Jicarilla Apache and Ute tribes and is still used for ceremonies.