I had to of course get some hiking in on my visit and went to the AMAZING Boulder Cave with my father!! Boulder Cave is the largest, most extensive cave of its kind. It took millions of years of volcanic action to create this landscape. Over thousands of years, lava flows occurred periodically in the Yakima basin and covered deposits of soft, loose rock and soil. The lava cooled, forming hard layers of basalt, and trapping the softer layers of loose sediment between. The water is now carving though soft sedimentary layers of loose rock, soil, and ash deposited between lava flows. The stream is busy cutting out a new cave. If you are ever in the Wenatchee National Forest it is a definite must see!!! Enjoy!