Most sailors will have a handheld GPS. In addition to Geocaching, you could also use it for inland exploration. Why not go bushwacking and find some hotsprings?
I have loaded the coordinates of California hotsprings to the site. Original data is from the National Geophysical Data Center, munging by me. KML format for Google Earth is here, GPX format for GPS software is here. Right click and “Save As…”
Thank you for creating this!