Boulder Cave formed more than 10 million years ago through a unique process. When the Yakima Basalt Formation — a series of lava flows with sediment deposits — covered the area. Devil Creek eventually eroded these deposits, causing sediment to collapse and the caves to form.
A short hike to the natural wonders left behind by the erosion process makes this trail popular on summer weekends.
The trail to Boulder Cave was built by the Civilian Conservation Corps (CCC) in 1930s and has been improved several times since then, most recently in 2014. The trail is signed as the Sun and Sage loop and it follows a small ravine. Make sure to keep an eye out for the lookout platform over the gorge just after the first hill. The path climbs gradually with a number of interpretive signs about the local ecology and history along the way.
As the trail flattens out, look to the far side of the ravine to see a new cave beginning to form. Then wind your way down to the the cave entrance. This cave formation is more of a tunnel so the trail through is one way, follow the sign to the right and the cave entrance.
If you plan to walk through the cave don't forget a light source or two. Also this area is important habitat for the Pacific western big-eared bat, please follow these guidelines to reduce disturbance to this sensitive species:
- Limit all noise (whisper)
- Stay on trail
- Don't touch the cave walls
- Direct light beam at the trail, avoid directing it at the ceiling
- Respect the seasonal closure
After you have explored this small cave (about 400 feet deep) you will pop out the backside and meet up with the trail. Head back out the way you came.