This mine, just a short trip along the road out of Firewatch, contains over 60 rubies (somewhat random due to use of raw ruby deposits that give a variable ammount). There's no owner attached, and no scripts to indicate a gotcha. At level 2, there were only easily defeated animals in the cave, including a mudcrab that I don't think belongs, and the only opposition was a scamp outside (which my unprepared mage easily defeated).