In the Cascades Range of Washington and Oregon, and to the east of these mountains, you are likely to encounter one or more species of energetic, small-ish, diurnal rodents.
My guess is that most people would point to any one of these rodents– at least one of the stripey species– and call it a ‘chipmunk.’ I did a quick Google Image search for ‘chipmunk Oregon’ and the results included many photos of ground squirrels.
There are indeed several chipmunk species in central and eastern Washington and Oregon. But there are also ground squirrels. No less than 12 species of ground squirrel live in this region.
Most of the ground squirrels are easy to distinguish from chipmunks because they (the squirrels) lack stripes, having relatively uniform coat colors.
All of the chipmunks have alternating light and dark stripes that run the length of their bodies, from nose to rump.
The squirrel most likely to be mistaken for a chipmunk is the Golden-mantled Ground Squirrel (Spermophilus lateralis). This species has stripes on its body and coloration that is remarkably similar to those of the Yellow-pine Chipmunk (Tamias ameonus) and the Least Chipmunk (Tamias minimus).
The Golden-mantled Ground Squirrel is larger (11-13 inches, including the tail) than the chipmunks and, importantly, does not have stripes on its head.
Look at the animals’ heads in the photos above and you will see the difference in striping.
There are actually two species of golden-mantled ground squirrel. The Golden-mantled Ground Squirrel (Spermophilus lateralis) is found in Oregon and the far east of Washington, whereas the Cacade Golden-mantled Ground Squirrel (Spermophilus saturatus) lives in the Cascades Range of Washington.