Pelage tawny to olivaceous; stripes obscure and underparts tawny, or stripes conspicuous and underparts white; tail slender and sparsely haired; size large; skull largest in the subgenus _Neotamias_. Baculum: Shaft thin; keel low, 1/5 of length of tip; tip 32 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/5 of shaft slightly compressed laterally; base deeper and wider than shaft; shaft short, 2.24 mm. Differs from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in base not markedly widened, shaft thinner, tip proportionally shorter; from _E. quadrivittatus_, _E. ruficaudus_, _E. cinereicollis_, and _E. quadrimaculatus_, in shaft thinner, baculum shorter and smaller; from _E. sonomae_, in ridges on either side of tip not enlarged, keel proportionally higher; from _E. amoenus_ and _E. dorsalis_, in base widened and thickened, baculum usually shorter; from _E. merriami_, in being markedly shorter, and having base widened and deepened but not incised dorsally. For comparisons with _E. alpinus_ and _E. minimus_ see the accounts of those species. _Specimens examined_: 2. _E. townsendii townsendii_: Oregon: _Multnomah Co._: Portland, 1 (NM). _E. t. cooperi_: Oregon: _Hood Co._: Brooks Meadow, 4,300 ft., 9 mi. ENE Mount Hood, 1. #Eutamias sonomae# Grinnell Figure 4 Upper parts rich reddish, more or less dulled by gray; backs of pinnae of ears nearly bare; tail long and bushy; size large; skull large, long, and narrow; rostrum deep. Baculum: Shaft thin; keel low, 1/10 of length of tip; tip 27 to 31 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/4 of shaft slightly compressed laterally; base deeper and wider than shaft; shaft of medium length, 3.03 to 3.30 mm.; ridges on either side of tip strongly developed, partly obscuring keel from side. Differs from _E. speciosus_, _E. panamintinus_, _E. umbrinus_, _E. palmeri_, and _E. bulleri_, in ridges on either side of tip strongly developed, shaft thin, base not markedly widened, tip proportionally shorter; from _E. quadrivittatus_, _E. ruficaudus_, _E. cinereicollis_, and _E. quadrimaculatus_, in shaft thin, ridges on either side of tip strongly developed, baculum shorter; from _E. amoenus_ and _E. dorsalis_, in keel lower, ridges on either side of tip strongly developed, base thicker and wider; from _E. merriami_, in markedly shorter, ridges on either side of tip strongly developed, tip proportionally longer, base wider and deeper but not incised dorsally. For comparisons with _E. alpinus_, _E. minimus_, and _E. townsendii_, see the accounts of those species. _Specimens examined_: 5. _E. sonomae alleni_: California: _Marin Co._: Unspecified, 1 (NM). _E. sonomae sonomae_: California: _Siskiyou Co._: Salmon Mts., W slope, W of Etna, 1 (BS). _Shasta Co._: Redding, 1 (BS). _Mendocino Co._: Cahto, 1 (BS).