GEOGRAPHY AND EVOLUTION IN THE POCKET 
GOPHERS OF CALIFORNIA’ 
By JOSEPH GRINNELL 
[With 1 plate] 
The most universally distributed type of rodent in California is 
the pocket gopher. It is found thriving at and below sea level, 
around the southern end of Salton Sea in Imperial County, and 
above timber line, at 11,500 feet altitude in the vicinity of Mount 
Whitney; it is found from the arid desert mountain ranges of the 
Inyo region, such as the Panamint Mountains, to the rainy and 
foggy coast strip at Humboldt Bay and Crescent City; it is found 
in the yielding sands of the Colorado River delta at the Mexican 
line and on the Modoc lava beds at the Oregon line. 
This fact of occurrence far and wide might seem to indicate a broad 
tolerance, tolerance of a number of conditions each varying between 
wide extremes. How is such an interpretation to be harmonized 
with the obvious fact that the pocket gopher is an exceedingly 
specialized type of rodent? Does not specialization ordinarily bring 
great restriction in habitat? A truism is this statement: The 
pocket gopher stock has solved successfully the problem of meeting 
the essential conditions of existence, else its racial line would not 
have persisted to the present day. Among races of animals the law 
is evident that only those budding forms persist and continue to 
evolve that are able to find suitable places, niches for themselves, in 
the economy of animal existence that are not already preempted 
and successfully occupied by other forms. 
The pocket gophers are rodents restricted to the Western Hemi- 
sphere; not only that, they comprise a family (Geomyidae) restricted 
to the continent of North America; furthermore, that family cen- 
ters in the southern half of the continent. The family Geomyidae 
contains several subdivisions—genera, in the parlance of the sys- 
tematist. The genus Zhomomys, to which all the gophers of Cali- 
fornia belong, is still further restricted to that portion of North 
America lying altogether west of the Mississippi River, and be- 
tween the twentieth and fifty-fifth degrees of latitude. As to origin, 
1 Reprinted by permission from the University of California Chronicle, July, 1926. 
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