According to the rulings on Gatherer, Blood Moon removes all abilities from nonbasic lands: a Forsaken Sanctuary will enter untapped, and will not tap for white or black.
My question, though, is—why? The rules text says only that "nonbasic lands are Mountains", which seems like it sets subtypes, but doesn't do anything about abilities.
I know that some abilities, like Forests tapping for green, are inherent to their subtype, so it makes sense that an Indatha Triome can no longer tap for green (the ability came from the Forest subtype, and it lost that). But I'm unclear on why changing a land's type removes abilities printed on the card itself.