The Geology and Petrography of Crater Lake National Park, 1902
LAVAS OF MOUNT MAZAMA.a
GROUSE HILL DACITE FLOW.
Possibly of about the same relative age is the Grouse Hill flow, which crosses the crest a short distance northeast of Llao Rock. On the inner slope the layer of pumice beneath the great flow of Llao Rock overlaps the Grouse Hill flow, showing that the Grouse Hill flow is older than the Llao Rock eruption. For this reason the two flows are separated on the map. At the south base of Grouse Hill the dacite (107) is regularly banded, and on the hill next northeast of Llao Rock it (108) is spherulitic. This flow has been much eroded, and has a more ancient look than other flows of this portion of the rim.