Mono Craters

Illustrating several stages in the formation of volcanic cones, this range extends in a gentle arc 16 kilometers (10 miles) southward from Mono Lake. The highest cone rises some 820 meters (2,700 feet) above the valley floor.

These cones date back to the late Pleistocene when Lake Russell, ancestral Mono Lake, was at a high level. Volcanic activity here has continued to relatively recent times. Panum Crater, just south of the lake, shows no evidence of shoreline cuts; and moraines of the Tahoe period are covered by pumice. Thus some of the craters date to no more than 9,000 to 12,000 years ago and may be more recent.

Most of the craters have followed a similar pattern of development: first there was a series of explosions which formed shallow, bowl-shaped depressions; following these, low-explosion cones were formed, made of rhyolitic pumice formed by the fragmentation of highly gas-charged lava; later, slightly viscous but mostly solid, cylindrical columns of obsidian arose in the craters to varying heights. If these obsidian domes were sufficiently elevated and contained enough molten material, lava would spill over the rims of the craters and form short flows with steep sides and fronts called coulees. In the mid-north and mid-south sections several of these flows joined to form extensive coulees. As the domes cooled, the obsidian fractured, aided by frosts, forming a talus which covers the slopes of most of the higher domes.

The Punchbowl, near the southern end, is a well preserved explosion cone with a crater some 360 meters (1,200 feet) in diameter and 42 meters (140 feet) deep. At the bottom is a small obsidian plug 75 meters (250 feet) across and rising 12 meters (40 feet) above the crater floor. Two nearly complete pumice cones may be seen near the summit just north of the southern coulee. Panum Crater and its neighbor to the south illustrate a more advanced stage of development. In Panum the steep-sided obsidian plug has risen to about the level of the crater rim from which it is separated by a moat. The Caldera, at the south end of the range, is the result of an explosion at the end rather than the beginning of the cycle; here the tops of the obsidian cliffs are covered with 10 - 15 meters (30 - 50 feet) of volcanic ash.

There is a Jeffrey pine forest, Pinus jeffreyi, surrounding the craters except on the pumice flats where there is sparse vegetation. The rare Astragalus monoensis occurs in the area.

Integrity: A portion of the east side has been scarred by quarries and there are poor roads in the range. An aqueduct tunnel pierces the range north of the Caldera.

Use: Research, educational

Ref: Hinds, N.E.A., 1952. Evolution of the California Landscape. Division of Mines Bulletin No. 158, p. 76 ff.
Kistler, R. W., 1967. Structure and Metamorphism in the Mono Craters Quadrangle, Sierra Nevada, California. United States Geological Survey Bulletin No. 1221-E, p. E1-E53.

April 1975