1967] Willey & Willey — Populations of Grasshoppers 
53 
variants of the eastern South Rim demes. Red Rock Canyon 6 has so 
far been inaccessible to us at the proper season. The East Portal 
deme 6 at the river’s edge has its peak too early in June for researchers 
with academic responsibilities, but a count of the last survivors on 
the south side of the river in mid-June, 1966, showed 10 yellow and 
2 orange, whereas a deme at the head of Spring Gulch (#28) across 
the river and one mile north-east was >99% orange (11=262) and 
less than a mile south of the river at the head of East Portal Canyon 
(#9) the population was 94% yellow (11=187). The river-edge 
populations at the confluence of Blue Creek and Curecanti Creek are 
inaccessible so far because of the seasonal factor and the construction 
of Morrow Point hydroelectric dam. However, the map (fig. 4) 
indicates that here, too, is a probable crossing point because of the 
similarity of population proportions. There is continuity of marginal 
habitat, also. Undoubtedly there is a strong influx of genes for yellow 
wing color from Soap Creek Valley, as well. 
At all other points we have found gulches, such as Dead Horse 
Gulch (#26) on the North Rim, which reach the river with fairly 
continuous habitat, but the opposite wall rises as a jumble of bare 
rocks and precipitous cliffs, creating an effective barrier to further 
movement. The banks of the river are either overgrown with brush, 
blocked with talus or composed of gravel bars with no grassy openings 
larger than a few square yards. High water marks 5 ft above the 
June water level indicate early spring flooding of the banks with 
accompanying great turbulence, making it unlikely that overwintering 
nymphs could survive on the infrequent sandy shores of the river. 
In addition to the effect of distance and difficult terrain, the effect 
8 We were able to study the early populations during May and June of 
1967. Results pertinent to this report are as follows: 
a. Head of Red Rock Canyon, 6700-6780 ft., 100% orange-red (n=109), 
May 8 (May 9 transect of canyon to Gunnison River yielded 100% 
orange, n — 25). 
b. East Portal at Gunnison River (locality #10) 47% orange (n = 58), 
May 7. 
c. Pioneer Lookout (locality #35), 100% yellow (n=128), June 5. 
The unexpectedly equal proportions of orange and yellow at East Portal 
indicate downward gene flow from both rims along the side canyons 
near this point with significantly less upward flow'. It is doubtful that there 
is an important additional pathway along the river, due to the apparently 
great discontinuities of suitable habitat. 
Explanation of Plate 7 
The Black Canyon Area. The section within the marked rectangle is 
shown in greater detail in Fig. 1. Numbers correspond to the locality 
numbers in the table, Fig. 2. Ideas on format thanks to Wallace Hansen. 
