Obsidian is the result of volcanic lava cooling rapidly when in contact with air or water, producing a dark glassy rock. It can be chipped to create very sharp edges. Deposits of obsidian are found on the northwest edge of the park and elsewhere in the Jemez Mountains.
Obsidian is very hard and brittle. Since it can be chipped to create sharp edges, it was important for making hunting points and cutting tools. Because it was readily available from the Jemez Mountains, it was an important trade item.