All, the reason that there are undercuts in large quantities in the east as opposed to the west is exactly the geology. Limestone, sandstone and shale are sedimentary rock and as such, weather very differently than igneous rocks such as granite and basalt. Both rocks react differently to the effects of water - sedimentary rocks have a high carbon content from the organic material that was compressed to form the rock and may cleave easily depending on the density and composition of the rock. Igneous rocks generally are highly compressed from the internal pressures of the earth and have no layering of materials that cause cleaving in sedimentary rocks. A great example of this is the granite all throughout the rockies - far less cleaving and undercutting. Also, the dramatically increased precipitation in the east as opposed to the west causes a much increased weathering of the eastern rocks. The eastern appalachian mountains are also far older and more weathered than the rockies and cascades of the west and obviously have a different composition that encourages undercutting.
I have worked on rivers throughout the country and I can tell you, knowledge is power. Study the rivers that you run, learn the hazards, keep your safety training current and keep your gear and your wits in good shape. There was a post on the buzz talking about a cook who came from Aspen and claimed that the people in West Virginia are ignorant. Just like anywhere else, if you take the time to think about the world that we live in, you'll find the knowledge that will help you along in this life. Like the old saying goes, failing to prepare is preparing to fail. If you don't educate yourself and manage the risks that you take, then you will end up like many people - in West Virginia or West Africa for that matter - ignorant of the world around you and therefore unprepared.
My deepest condolences go out to the families of the river runners that have died on the Gauley, as much as I love the canyon, I was sure upset on Sunday with the news of the fatality and even more upset to learn that a fellow Ocoee guide died on Monday after I was off the river and on the road. Y'all take good care out there and be well!