Board Thread:Naruto Discussions/@comment-24120130-20140725123237/@comment-945885-20140827090851

Mount Myoboku, Ryuchi Cave, and Shikkotsu Forest are the ancestral grounds of the frogs, snakes, and slugs. The places are legendary, but hidden.

As far as I understand it, the training is how they learned to use Sage Mode, and the locations are nothing more than where they found individuals to train them. The reason their Sage Modes differ is in the technique, not the location.

In my opinion, he's not saying that Jugo's clan's kekkei genkai literally has their origins in Ryuchi's cave, but rather that their kekkei genkai is a passive, naturally occuring form of Sage Mode; Orochimaru wasn't interested in their kekkei genkai, he was interested in Sage Mode.