Canyon, 101 river miles above the mouth of the river, Hebgen Reser- 

 voir backs up to the Yellowstone National Park boundary. 



From the headwaters in Yellowstone Park, the Madison flows 

 across a high plateau to Hebgen Reservoir. Downstream from Hebgen, 

 it flows through the Madison Canyon ^frontispiece) for about 8 miles 

 and thence into the upper Madison Vaxiey (Figs. 1 and 2) for a dis- 

 tance of about $0 miles. The gradient in the upper valley averages 

 about 29 feet per mile. The continuity of the upper Madison Valley 

 ends abruptly at the head of Bear Trap Canyon, at the lower end of 

 Madison Reservoir. Bear Trap Canyon (Fig, 3) is a 'narrow gorge about 

 11 miles in length. Leaving Bear Trap Canyon, the river flows for 

 about 20 miles through the lower Madison Valley to its juncture with 

 the Gallatin and Jefferson Rivers, The gradient of the river in the 

 lower valley is about 16 feet per mile. The Madison drains an area 

 of about 2,500 square miles. 



Flows in the Madison River were once subject to considerable 

 variation but now are largely controlled by operation of Hebgen and 

 Madison Reservoirs. Normally, low flows occur in the winter and 

 high flows in June, although, depending on weather conditions, maxi- 

 mum flows sometimes occur as early as March or as late as July. 

 Normal flows during the summer period are about 2,000 second-feet. 

 The more or less constant flows are an important factor in making 

 the Madison River a good trout stream. 



The bed of the river is composed largely of rubble and 

 boulders (Fig. 1), however gravel or sand bars suitable for spawning 

 sites are common. Except in the extreme lower section, the river is 

 characterized by riffles and rapids (Fig. 3). The frequent large 

 boulders in the channel afford cover for the fish„ Many small islands 

 in the stream between Madison Reservoir and the town of Ennis improve 

 the habitat in this area (Fig. 2) . Large pools occur in the area 

 just above the town of Three Forks. The river varies in width from 

 about 200 feet in Madison Canyon to about 300 feet below Madison 

 Reservoir, 



Water temperatures were taken at 8:00 a,m, daily during the 

 period of study. In the Lower Section (1950), the average tempera- 

 ture was about 60° F, The recorded maximum and minimum were 70° F. 

 and k0° F., respectively. In the Middle Section (1951), the seasonal 

 average was 51° F. The recorded maximum was 67° F. Water tempera- 

 tures exceeding 60° F. were recorded on only 6 days during the 1951 

 study period. In 1952, a maximum temperature of 6h F. was reached 

 in Madison Canyon in August. The average for the period between 

 mid-July and mid-September was about 60° F. ; the seasonal average 

 was 55° F. Twenty miles below Madison Canyon, the seasonal average 

 temperature was about 50° F. The lower seasonal average for the 

 area below the canyon may be attributable to inflow from numerous 



