The fact that rare earths have been so cheap from countries like China, where no environmental restrictions apply, has meant there has been no exploration for deposits in the USA for years. Geologists don’t sit around waiting for the next boom to occur, they go into other careers.
You may find this interesting:
World Resources: Rare earths are relatively abundant in the Earth’s crust, but discovered minable concentrations are less common than for most other ores. U.S. and world resources are contained primarily in bastnäsite and monazite. Bastnäsite deposits in China and the United States constitute the largest percentage of the world’s rare-earth economic resources, while monazite deposits in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the United States constitute the second largest segment. Apatite, cheralite, eudialyte, loparite, phosphorites, rare-earth-bearing (ion adsorption) clays, secondary monazite, spent uranium solutions, and xenotime make up most of the remaining resources. Undiscovered resources are thought to be very large relative to expected demand.
http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/mcs-2010-raree.pdf
The name rare earths is a misnomer because they are not all that rare. It is just that you seldom find commercial grade deposits of elements that so readily substitute into other minerals. A mineral deposit is a freak occurrence in nature because normally earth processes disperse elements, not concentrate them. For instance, gold is everywhere in the earth’s crust and water, but seldom in concentrations that allow economic production.
I agree that there probably hasn’t been all that much exploration (and thus, discovery nor enumeration) for REs per se in the US. So, their prevalence is at least partially an unknown. However, where we find most of our non-ferrous goodies in the US = the West, *has* been widely though certainly not exhaustively explored. So the odds are shrunken that we’ll find anything monumental. Sure, there’s always the possibility of finding a mother lode somewhere, but it’s not a great bet.
Still. Never mind the eco considerations, mining exclusively for REs seems pretty far fetched in terms of economic viability within the US. Monazite is generally known as home of Thorium. If we were mining thorium, we’d be getting REs along with the thorium. But we’re not with any great gusto.
I don’t especially agree that they are relatively abundant, even if the WRC says so. The rare earths are 17 elements and ALL OF THEM, taken together, might be a little less rare than “rare” but getting any particular ONE of them, the one you need, remains a needle-in-the-haystack affair. They are usually grouped all together in the type of generalistic reports you linked and IMO that gives the impression they are statistically more common than they are in reality.