Sand Mountain Field

The Sand Mountain volcanic field consists of 23 basaltic and basaltic andesite cinder cones along a N-S line immediately west of the Cascade crest NW of Mount Washington. Two cone alignments trending NNW and NNE intersect near the largest cinder cone, Sand Mountain. Although previous radiometric dates spanned a range of more than a thousand years, tightly constrained paleomagnetic ages imply that at least 13 eruptive units were emplaced in a relatively short period of time about 2,950 years ago lasting at most a few decades.

The Jack Pine vent at the northern end of the field is compositionally distinct from the rest of the volcanic field and is considered to have been erupted about 4,000 years earlier. Lava flows traveled predominately to the west, blocking local drainages and forming several small lakes.