Boulder Cave

Useful Information

Location: East of Ellensburg, northeast of Yakima, east of Mt. Rainier.
I82, turn off atnorth Yakuma onto Hwy 12 west 25 km turn right onto Rd 410, 32 km then turn left across Naches River onto Old River Road. Signposted. 2.5 km walk to the caves.
(46°57'8.89"N, 121° 5'10.03"W)
Open: APR to OCT daily . [2007]
Fee: Cave: free.
Paring: Car USD 5, Bus USD 15.
Classification: SpeleologyTectonic cave
Light: none, bring torch
Guided tours: L=120 m.
Address: Naches Valley Chamber of Commerce, P.O. Box 881, Naches, WA 98937, Tel: +1-509- 653-2165 (RJ's Tires - ask for Randy). E-mail: contact
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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1920s the Forest Service had created Boulder Cave Recreation Area.
1935 the CCC built a group shelter with a large stone fireplace.


Boulder Cave is a tectonic cave, a result of collapse, but caused by erosion. Devil's Creek, a small river, a tributary to Naches River, cut into the lava layers of Washington State. Two layers or rather hard basalt have a thick layer of tufa or sediments inbetween. The river eroded the soft tufa much faster and thus formed a sort of long ledge, a deep notch along the river bed. But once a piece of the overhanging roof collapsed, the fron fell down to the floor, the back stuck on the wall. The result is a 120 m long almost straight tunnel with a triangular profile. Devils Creek still flows through the cave.

This cave is a bat cave, it is inhabited mostly by Pacific Western big-eared bats. Originally thousands of bats hibernated in this cave, but this number dropped after the 1920s which corresponds with a drastic increase in visitation. The big-eared bat is extremely intolerable to human disturbance. Today the cave is closed during winter for hibernation, so the number of bats turned upward. At the moment a small population of some 50 bats use Boulder Cave as a hibernaculum.