Ruins

Ruins are probably what is remaining of what used to be a settlement or an outpost.

When a player finds a ruin, they may look what is inside. Ruins contain Mars Dollars, but they leave equal to less than what volcanoes contain. Like volcanoes, motherlodes can be found, and the amount of Mars Dollars found in a motherlode possibly ranges from 80-160 Mars Dollars, and unlike volcanoes, there is no way to lose Mars Dollars when looking through a ruin. There are more volcanoes than ruins, though.