It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite,
sandstone, Rhyolite, marl, and basalt.
This sounds perfectly plausible, but the issue is that while Rhyolite, which forms the bedrock on top of which the river system is located,
is a volcanic rock, it doesn't form lava tubes.