1967] Willey & Willey — Populations of Grasshoppers 
57 
venient marker (wing color) is available which may have been segre- 
gated in the source populations elsewhere in the Gunnison Basin 
during the Pleistocene. The evidence is circumstantial that the 
northern orange and southern yellow populations reached the Black 
Canyon area after the canyon had acquired its present form. The 
clinal variation between demes of the South Rim may be due to 
southward gene flow of orange- wing across the river at the western 
end of the canyon and slow lateral movement along the rim. The 
slow speed of gene flow seems to be due to the sedentary behavior 
of the adults, spatial discontinuities in suitable habitat and seasonal 
differences between the rims and the river 2000 ft. below. 
Acknowledgements. 
We are grateful for the aid of David Werner, Darelyn Weber, 
Ruth Lewert, Allen Berlind, and Joyce Redemske, our assistants for 
at least one of the years of study; the Rangers of the National Park 
Service, particularly Jack Fewlass, Wilton Hoy and Supt. Henry 
During; and the ranchers who gave us information and permission 
to enter their land for this study, particularly Joseph Eisaguirre, 
John Leonard, Octave Nicholas, Clarence Sanburg, Milton San- 
burg, and Russell Sanburg. We thank James Seery, Project Con- 
struction Engineer for the Bureau of Reclamation, for allowing us 
access to East Portal while construction for Crystal Dam was still 
underway. Wallace R. Hansen of the U. S. Geological Survey offered 
helpful suggestions on the format and background of Plate 7 and 
kindly gave us permission to modify Fig. 15 of Geological Survey 
Bulletin 1191 for Fig. 1 of this paper. We would also like to thank 
Dr. Eliot Spiess who read the manuscript and offered constructive 
criticism. 
This work was supported in part by grant GB-2201 of the 
National Science Foundation, grants from the Research Board of 
the University of Illinois, and a Sigma Xi-RESA Grant-in-Aid of 
Research for the summer of 1963. 
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Hall, E. R. and K. R. Kelson. 
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Hansen, W. R. 
1962. The Black Canyon of the Gunnison, Today and Y esterday. U. S. 
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1965. Glaciation of the Rocky Mountains. In Wright, H. E. and D. G. 
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