Hayfork is a census-designated place (CDP) in Trinity County, California, United States. The population was 2,368 at the 2010 census, up from 2,315 at the 2000 census. Hayfork was originally named Nor'el pom, after the Native American tribe that lived in the area.
The community was so named on account of hay fields along the east fork of the south fork of the Trinity River.
Hayfork is located at 40°34′17″N 123°8′48″W (40.571406, -123.146619) at an elevation of 2310 feet.
According to the United States Census Bureau, the CDP has a total area of 72.1 square miles (187 km2), of which, 72.1 square miles (187 km2) of it is land and 0.02 square miles (0.052 km2) of it (0.03%) is water.
This region experiences warm (but not hot) and dry summers, with no average monthly temperatures above 71.6 °F. According to the Köppen Climate Classification system, Hayfork has a warm-summer Mediterranean climate, abbreviated "Csb" on climate maps. Hayfork experiences extreme diurnal temperature variation in summer, and also in winter the diurnals are wide enough to cause significant air frosts during night. Atypical for an area with such hot summertime temperatures and mild winters, frost usually occurs from mid September to early June, and frosts throughout the summer are not unheard of. There are an average of 69.8 days with a high over 90 degrees Fahrenheit, and 155 days that go below 32 degrees, including 1.7 days in June. On average, once every 10 years there will be a frost in July and 3 out of 10 years there will be one in August. Three times every ten years the temperature drops below zero.