[1] The Ukiah Valley extends up the Russian River to the junction of the east fork with the main stream.

The East Fork of the Russian River has a youthful topography, flowing with a high gradient through a V-shaped gorge.

Cold Creek flows at a much lower gradient, as is shown by the size of stones in its bed, and has a distinct flood plain and also a terrace.

This is plausible, since there have been tectonic events in the region and Clear Lake is 600 feet (180 m) higher than the Ukiah Valley.

[14] Before the Eel River water was diverted, the East Fork would nearly dry up in July, August and September.

A flour mill in Coyote Valley on the East Fork had water to drive its wheel carried from Cold Creek, which runs year round, along 1.5 miles (2.4 km) of flume.