Google Earth (satellite imagery) is a fantastic boon for anyone interested in geology. But of course these images don't show enough detail to really work out what is down there. The TourBuilder App (running on your smartphone) lets you collect data at the coalface (if you'll excuse the pun) and later marry it up to the satellite overview. Or take samples and allow others to return to the exact same spot. More than showing the location on a map, it shows others how to access that location. Of course you can add photo's, video or audio tied to specific locations.
TourBuilder is FREE. It runs on any Android device, all iPhones and iPads.
TourGuide is FREE and available for Android, iPhone and iPad. All of the tours are Free to download.