THE GROUND SQUIRRELS OP CALIFORNIA. 663 



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Fig. 21. Plot of a used burrow belonging to a 

 female Belding Ground Squirrel, as excavated by 

 J. Grinnell and T. I. Storer in a meadow near the 

 Tioga Road, on Snow Flat, 8,700 feet altitude, 

 Yosemite National Park, June 2 8, 1915. 



Main opening of burrow at a (down this the 

 squirrel went when shot, and was subsequently 

 found at c) ; two other openings at a' and a" ; at h 

 and 6' blind branches directed downward (the squir- 

 rel may have essayed to dig deeper at these points 

 but was discouraged by water) ; food materials, 

 including lily tubers, in chamber at f ; in the enlarge- 

 ment at the point marked nest was an accumulation 

 of dry grass, the remains of an old nest or the 

 beginning of a new one (the young would not have 

 been born for about two weeks) ; boulder at g 

 bulged out over the portion of the burrow adjacent 

 to it, affording protection to the supposed nest- 

 chamber. 



Diameter of burrow, 45 to 65 millimeters; average 

 Df several measurements, 52. Average depth beneath 

 surface of ground, about 135 mm. Greatest depth, 

 at h and h', 330 and 270, respectively. Total length 

 of system, about 54 feet. 



The burrow system above described belonged to just one squirrel, an 

 adult female, which was found to contain five embryos, the only exact 

 evidence we have as to the number of young to a litter. This was at 

 8,700 feet altitude, on Snow Flat, Yosemite Park, on June 28. Half- 

 grown young were common on Tuolumne Meadows, 8,600 feet, July 16. 

 Young two-thirds grown have been taken at Independence Lake, Nevada 

 County, 7,000 feet altitude, as early as July 13. Three third-grown 

 young were seen, and one of them photographed (fig. 22) , at 6,800 feet 

 altitude near Williams Butte, Mono County, June 28. There is thus 

 probably some variation in time of appearance of the young, with alti- 

 tude, the animals at the highest levels being born latest in the season. 

 The young are out quite generally by the 15th of July. Only one litter 



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