196 TRANSACTIONS OF THE 
by low vegetation will be about one-third the precipi- 
tation received, and in an evergreen forest about one- 
tenth the precipitation. Assuming a Utah mountain side 
to receive an average of 12.00 inches of precipitation 
in a summer, the forest areas would lose only 1.20 inches. 
The greatest influence of the forest in this general 
respect is in controlling or modifying the streamflow. 
The spring freshet curves are greatly flattened, and the 
late summer depressions due to droughty weather are 
appreciably raised. The feeder streams that live through 
the summer, originate in the forests, as all fishermen and 
outdoor men well know. 
The cooler weather in the forests retards the melting 
of the snows, and there is much less sunshine because 
the forests of Utah lie chiefly on the northerly slopes, 
away from the sun. Many glacier-like piles of snow 
accumulate in the lee of high ridges, and especially in 
amphitheatres from which several slopes shed their 
snowslides. The seepage from these piles of snow in 
important locations, like the district near Spanish Fork 
Mountain, maintains a thin cluster of trees a short distance 
below the tail of the snow pile. However, even assuming 
the drift to be several acres in extent, thirty to forty feet 
deep, and of a density of 60% to 75% at most, the actual 
number of acre-feet of water is not great, as compared 
with the snowfall over the watershed as a whole. 
Forests retard surface runoff by offering material 
obstruction to the flow, and by preventing gulleying and 
hence the formation of large heads of water. They serve 
also to filter and purify to a certain extent, the water 
collected in the basins. At Jacob’s Lake Ranger Station, 
on the Kaibab National Forest in Arizona, an unusually 
heavy downpour of rain caused broad sheets of water 
broken up by small waves, to advance from the forest to a 
natural reservoir. 
The pine cones, needles, small sticks and grass 
served to keep the flowing water divided into relatively 
thin streams, though tiny white caps piled up everywhere 
as the heavy flow was temporarily blocked by the debris, 
here and there. After the storm ceased the pool of water 
was scarcely riled, and nearly clear. 
Our camp on the previous night, at a desert watering 
