37 Inter-andesitic Dacite Pumice on the Caldera Wall

The section at Cottage Rock (see figure 7) is as follows, the series beginning at the top:1

a. The Cloudcap dacite flow.

b. Welded dacite tuff, similar to that of the Wineglass (page 60); 20 feet. This deposit is rich in angular blocks of andesite, and upward merges imperceptibly into the Cloudcap lava.

c. Pink and brown lump pumice; 3 feet.

d. Block layer consisting chiefly of lithic fragments of andesite in a matrix of dacite pumice; 4 feet.

e. Compacted, but not welded, pink and brown lump pumice crowded with fragments of andesite; 3 feet.

f. Well bedded, smoke-gray lump pumice with lithic blocks up to 2 feet across forming a fifth of the whole; 70 feet.

g. Uncompacted red, pink, and brown lump pumice with fewer lithic blocks; 50 feet.

h. Welded and streaked, red and black dacite tuff (ignimbrite), similar to the Wineglass tuff; 6 feet. This forms the conspicuous dark band at the base of Cottage Rock itself.

i. Unwelded, but compact, pink and brown lump pumice; 30 feet.

i. Strongly welded red, brown, and black tuff; 3 feet.

k. Buff and white, incoherent lump pumice with abundant lithic fragments; 10 feet.

l. Poorly exposed and doubtful glacial till; 10 feet.

m. Many flows of andesite, the four lowest of which are separated by layers of till.