Merriam (1905) was the first to show clearly that _Eutamias
quadrivittatus_ is a distinct species, and pointed out that _E.
amoenus operarius_ (= _E. minimus operarius_) is a small species
which resembles, and is found in some areas together with, _E.
quadrivittatus_.
Howell (1929) placed under _E. quadrivittatus_ the following
subspecies: _E. q. quadrivittatus_, _E. q. hopiensis_, _E. q.
inyoensis_, _E. q. frater_, _E. q. sequoiensis_, and _E. q.
speciosus_.
Hardy (1945) placed _E. adsitus_ under _E. quadrivittatus_ as _E. q.
adsitus_, and Kelson (1951) placed _E. umbrinus_ under _E.
quadrivittatus_ as _E. q. umbrinus_.
Johnson (1943) re-established _E. speciosus_ as a separate species,
and in California left only _E. q. inyoensis_ in _E. quadrivittatus_.
Thus, since 1943 the recognized subspecies of _E. quadrivittatus_ have
been: _E. q. quadrivittatus_, _E. q. hopiensis_, _E. q. inyoensis_,
_E. q. nevadensis_, _E. q. umbrinus_, and _E. q. adsitus_.