In an earlier post (Young Golden-mantled Ground Squirrels) I noted that golden-mantled ground squirrels look very similar to and are often confused with chipmunks (Tamias sp.). The most obvious difference in the field is that golden-mantled ground squirrels lack stripes on the sides of the head while head stripes are present in chipmunks.
There are eleven species of chipmunks in the Pacific States, some of which are so similar that the shape of incisors, characteristics of the bacula (the bone supporting the rigidity of the penis, only millimeters long in chipmunks) length of tail or other body parts and geographic and ecological distribution are used for identification. Given that the ranges of chipmunks overlap and I cannot measure feet, tails or bacula while wandering about with my camera I will simply identify these pictures as a chipmunk species. Pressured, I would guess this particular chipmunk, photographed at Medicine Lake CA, is a lodgepole chipmunk (T. speciosus).
Chipmunks are diurnal rodents. They primarily eat seeds and fruits although some species will eat insects, particularly in the spring. Chipmunks use their cheek pouches to carry and cache food. They do not put on fat for the winter. Instead chipmunks are partial hibernators and will waken and feed on their stored provisions occasionally throughout the winter. The food caches are also important in the spring when snow covers the ground and seeds and fruits are not yet available. Their nests are underground or in an abandoned hole (often a woodpecker hole) high in a tree.
Previously Eutamias was the genus name for chipmunks and is still found in the literature.