Glass Mountain


State-of-the-art Mill with rail and truck loading facilities.

Supplying light weight aggregate to industries throughout the United States. Large stockpiles of pumice provide customers with assurances that all products are available for immediate shipment. GMP ships lightweight pumice aggregate via rail and truck.

GMP will provide customers high quality materials for decades. GMP has the most extensive pumice reserves in the United States.


The Glass Mountain pumice deposit is located in the Medicine Lake Highlands, Tionesta, CA, high above the Klamath Basin, which is a topographically high region of recent volcanic terrain. The Medicine Lake Highlands is a shield volcano along the boundary between the Cascade Range to the west and the Modoc Plateau to the east. A caldera, approximately six miles across at its widest diameter, occupies the top of the broad shield volcano. Medicine Lake is within this caldera.

The Medicine Lake Highlands is one of four active volcanic regions in California. There are more than 100 volcanic vents on the flanks of the shield volcano, most of which are either silica domes or cinder cones with associated lava flows. There have been at least six documented eruptions in the past 2,000 years.

The pumice is less than 23,000 years old. The old trees found in the pumice and obviously killed by the pumice eruptions to be between 1,400 to 1,700 years old. The pumice erupted from vents close by, from the Glass Mountain area which is within one mile south of the mine. The thickest depth of the pumice is found to the south indicating the origin may be in that direction. Subsequent to the pumice emplacement, silica viscous glass flows come from vents on Glass Mountain, forming massive blocky flows of rhyolite, obsidian and rhyolite dacite. These flows terminate in the steep slopes along the southern margins of the claims where the pumice exposures terminate.

The pumice is an air-fall unit. It attains a thickness of up to 40' on the claim, where it is closest to the vent, down to less than three feet in thickness further away from the vent. The pumice is light grayish-white and ranges in size from blocks of several inches across to fines. The original terrain is blanketed by the pumice.