Erosion tends to produce tall, canyon-like passages. Some of the most spectacular erosional caves known are formed in granitoid rocks in some of the mountainous regions of the western United States. The five photos below are from one such cave system, where water has carved out almost a mile of canyon passage with deep potholes like the one below. Left , a caver uses the scalloping on the walls to climb over a deep pool. Center , two dikes cross in the passage wall.
Dikes are molten material intruded into cracks in the igneous host rock.
Right, the cave system in flood. Sand particles borne by floodwaters have played a large role in creating this system. In America's southwest there are large sandstone deposits. Note the large sand dune below the left-hand entrance.