According to the Wiki, they can and do generate at bedrock:
"When generated at bedrock layer Abandoned Mineshafts will cut through bedrock. It is currently unknown if it can cut through the last layer of bedrock."
That's handy, half of mine are a mess of parts cut off by ravines. I don't think I've seen one as neat as that before.
omg i know right i have this world were there is like a ravine that is like a giant X and scartterd all throughout it is like 4 giant mineshafts its AWESOME
"When generated at bedrock layer Abandoned Mineshafts will cut through bedrock. It is currently unknown if it can cut through the last layer of bedrock."
Great find, though.
Stay fluffy~
A lot of deeper ones have Bedrock under the lava...no-one ever looks, though....
Stay fluffy~
and 7 out of 10 steves die from mineshaft ravines.