EarthCache

I've long been a fan of one of the lesser known types of geocaching, the EarthCache.  Unlike their more well known counterparts, there is no container of tupperware hiding in the woods.  Instead, the cacher must visit a location for its geological significance and answer a few questions in order to log the cache as a find.  I've logged a bunch of them and set up three of them myself at some of my favorite geological spots.  I guess they bring together two things I'm passionate about:  Earth science and education. 
Last week I returned home from being gone for a month, where I was teaching geology field camp for Wheaton College at their science station in the Black Hills of South Dakota.  While out there, I was able to find several EarthCaches.  So far I've only logged a few of them, and I've got about a dozen or so more to go.  It can take a bit of effort to finish them all up, which is why a couple of other geocachers I know have said they hardly ever log them.  But I find them much more rewarding than the regular geocache. 
I found two locations while out there that will make for excellent EarthCaches.  I don't want to give too much of them away before I submit them, but one is an unconformity in the Black Hills and the other is a fault in the Bighorns.  More to come maybe after I get them submitted.