I did my undergraduate thesis on granite weathering. It was a natural progression given my teenage years hiking in the Rampart Range of Colorado: low mountains of deeply weathered granite. For those that don't know, the biotite in granites weathers into vermiculite. The change results in an increase in the volume of the mica, and it effectively shatters the rock. This progesses inward from joint surfaces, attacking the corners and edges, leaving a rounded form of solid granite. The process is essentially bimodal: outcrops are either solid rock or gravel (called "grus". The process, I swear, is called "grussification"). As the gravel is carried away, the "sphereoidally" weathered "core stones" can lag down upon each other, stacking up in really interesting piles.

Sometimes, the weathered joint surfaces are exploited by rivers or creeks, and since they are soft, the river can cut deep, narrow channels. The most famous of these is Lost Creek (in the Lost Creek Wilderness Area, SW of Denver) where the creek disappears for a mile or so into a deep cave carved into the granite. It's one of the biggest, and most dangerous, caves in Colorado.

Where is Enchanted Rock in Texas, in case I get down to the Lone Star State?