Fissure on Black Point Volcano, California by ahochstaedter

This is a fissure developed on the top of Black Point Volcano on the shores of Mono Lake, California. The walls of the fissure reveal near horizontally bedded layers of basaltic tephra. The gentle layering observed and all around Black Point Volcano support the notion that the tephra layers were deposited underwater. Rather than dipping away from the vent as they would on an on-land cinder cone, the gentle layering is interpreted as dispersal by water and more even deposition around the vent. White bubbly tufa on the walls of the fissures indicates that the fissures were formed while the volcano was still underwater or that it was resubmerged after formation.

Dating of these types of layers indicate eruption of the Black Point Volcano about 13,000 years ago.

A wide-view gigapan of an adjacent outcrop is here:
www.gigapan.org/gigapans/98271
Close-up views of the adjacent outcrop are here:
www.gigapan.org/gigapans/98272
zoom.it/lFot 
A view of Mono Lake from the top of Black Point Volcano is here:
www.gigapan.org/gigapans/98270
"Geology Underfoot in Yosemite National Park" by Glazner and Stock (2010) provides a fine synopsis of this field area.