The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams
The Climax: Culminating Explosions of Pumice and Scoria
Detailed Description of the Individual Flows
Having enumerated the general features of the glowing avalanches, we may now pass to an account of the individual flows.
The Rogue River Flows
The glowing avalanches that followed the Rogue River and its tributaries united near the confluence with Union Creek, and the composite flow continued for another 20 miles to a point 1 1/2 miles above the present site of the village of McLeod. The snout of this composite flow thus lies 35 miles in an air line from the former summit of Mount Mazama.
The following notes refer to the deposits found along the Rogue River from the vicinity of Diamond Lake to McLeod; the flows that ran down the tributaries of the Rogue are described in a later section. Although most of the flows of basic scoria which poured down the north slope of Mount Mazama through the depression between Llao Rock and Grouse Hill came to an end in the Pumice Desert, the earlier and more voluminous flows of pumice not only crossed the desert but surmounted the divide beyond, and some of them discharged into Diamond Lake. The bulk of the pumice then separated into two branches, one directed eastward toward the Klamath Marsh and the other westward down the valley of the Rogue. The latter branch was joined by flows which skirted the west side of Desert Ridge. As far down as the junction with National Creek, the deposits of the Rogue valley consist of buff and pale-gray dacite pumice unusually poor in lithic debris. In many places the river has cut through the deposits to the underlying basalts, as at the Upper Falls and in Hamaker Meadows. The great scarcity of charcoal among the ejecta in this region implies that this part of the Rogue River valley supported only a scant cover of trees at the time of the eruptions.
Where Copeland Creek enters the Rogue, the thickness of the pumice increases to almost 200 feet. Still farther south, the thickness continues to increase and locally approximates 300 feet. Along this stretch of its course, the river has cut through the deposits to the underlying intracanyon olivine basalts. Here also the pumice deposits are abundantly charged with burned wood. On the west bank of the river, a mile below the crossing of the Diamond Lake highway, Smith discovered at the base of the pumice an 8-foot stump of a cedar tree, 3 feet in diameter, standing upright in the position of growth. Its upper part was thoroughly charred, but the lower part, perhaps because of quick burial, was burned only a little. This is the only example known of an upright tree within the pumice flows. The rest of the charred wood occurs as scattered limbs and logs lying more or less prostrate.
