04 Distribution of the Pumice

Pumice Deposits of the Klamath Indian Reservation, Klamath County, Oregon

Distribution of the Pumice

Most of the many hundreds of square miles that comprise the Klamath Indian Reservation are covered either by pumice fall or pumice flow material. (See pl. 1.) The pumice fall was carried by the wind for great distances from Mt. Mazama and immediately after eruption it covered not only the entire Reservation, but also many hundreds of square miles beyond the limits of the Reservation. The pumice flows, on the other hand, moved relatively short distances, and therefore are found only on the flanks of the volcanoes and in the adjacent valleys. On the Reservation they are confined to the area west of Klamath Marsh.

Approximate thicknesses of the pumice fall is indicated by isopachs on plate 1. In the area south of Chiloquin, along the Sprague River valley, and near Sycan Marsh and Yamsay Mountain the pumice fall deposits are generally less than a foot thick, and in parts of these areas the thin layer of pumice has been completely removed by erosion. The pumice fall deposits in the area immediately east and south of Klamath Marsh range from 5 to 20 feet in thickness, and a few drifts may be as much as 30 to 40 feet thick. The average thickness of the pumice in this area is perhaps as much as 15 feet.

Pumice flow deposits completely cover the area to the west of Klamath Marsh. Their maximum thickness as determined from well logs, ranges from 47 feet near Kirk to 90 feet in sec. 18, T. 29 S., R. 7 E., about 6 miles north of Lenz. In most places, however, these deposits contain numerous interbedded lenses and layers of red or black scoria, layers of sand derived exclusively from volcanic rocks, and layers of gray cinders. These are undesirable from the standpoint of commercial exploitation of the pumice. Neither the distribution nor the thickness of the layers of intermixed material can be predicted with accuracy.

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