7860

• UCREFRP Catalog Number: 7860
• Author: Douglas, M. E. and P. C. Marsh
• Title: Population Estimates/Population Movements of
• USFW Year: 1996
• Copyright Material: YES

DOUGLAS AND MARSH-ESTIMATES/MOVEMENTS OF GILA CYPHA 17

Fig. 2. (A) Map of the Colorado River basin, depicting dams, reservoirs, and component rivers. (B) Map
of the lower Little Colorado River, from Blue Springs (21 km above confluence; Navajo Indian Reservation,
Coconino County, AZ) to its confluence with the Colorado River in Marble Canyon (Grand Canyon National
Park, Coconino County, AZ). Confluence is 99 km below Glen Canyon dam.

cussed in the context of Glen Canyon Dam, built
in 1963 to impound Lake Powell at the north-
ern extent of Grand Canyon.

MATERIALS AND METHODS

Stud)' river.- The LCR drains 141,155 km2 of
eastern and northern Arizona and western New
Mexico and flows 412 km from headwaters to
confluence with the Colorado River (GCNP,
Coconino County, AZ; Fig. 2). Unless in flood,
the LCR is seasonally dry in much of its upper
390 km, a result of modern land-use practices
and water impoundments initiated at the turn
of the century (Miller, 1961). However, flow in
the lower 21 km is perennial, from numerous
groundwater springs which drain 72,520 km2
of the Black Mesa north and east of Flagstaff,
AZ. The largest of these (i.e., Blue Springs, at
LCR RKM 21; Fig. 2B) has a discharge of 6.1-
6.6 m' /sec (Johnson and Sanderson, 1968).
The LCR at base flow is saline (conductivity
exceeds 5000 umhos/cm-') and travertine-
forming. Carbonate precipitates onto surfaces
and in the water column, the latter giving the
river a distinct turquoise color. Carbonate de-
position (a function of CO2 degassing and pho-
tosynthetic activity of algae and cyanophyceans)
produces an intricate and confusing water

chemistry (Kubly and Cole, 1979). Travertine
accumulations over geologic time define pools,
runs, and rapids and generate scalloped water-
falls and cascades. Interspersed amongst this
structure are broad sandbars and other depo-
sitional features more typical of erosive south-
western streams. These shift seasonally (and
dramatically) according to duration and extent
of flooding. Dominant riparian vegetation is a
mixture of native [Catclaw acacia (Acacia greg-
gii). Honey mesquite (ProsoPis qlandulosa). Coy-
ote Willow (Salix exigua), Arrowweed (Tessaria
sericea)] and nonnative species [Tamarisk (Ta-
11larix chinensis), Camel thorn (Alhagi camelorum);
Carothers and Brown, 1991; Johnson, 1991].
Giant reed (Phragmites australis) and cattail (Ty-
pha spp.) occur patchily. The lower LCR passes
through a narrow gorge that progressively wid-
ens and deepens as it drops toward Marble Can-
yon. A series of precipitous travertine falls at
RKM 14.9 (Atomizer Falls, Fig. 2B) mark up-
stream distribution of G. cypha.

Base camps.- Three base camps were estab-
lished in the LCR gorge: near its confluence
(RKM 0.55); at Powell Canyon (RKM 3.1); and
at Salt Canyon (RKM 10.8). Biologists worked
from each camp. Those at the confluence fished
the lower 1.2 km of river, whereas those at Pow-