What's probably just a little ways down out there is most likly some sort of lava - If when you said 'tuff' you were giving me the name of something - Yes, tuff is basically from pyroclastic flows - stuff from ash and molten lava..

Here's a formal definition:
Tuff is lithified volcanic ash. It contains a variety of small angular fragments that were blown out of the volcano into the air. As the fragments fall, the larger and heavier ones fall faster and the tuff may show layering like a sedimentary rock.

The whole area out there has a lot of volcanic substance in it.

Canie