Mad River (formerly, Kuntz) is a census-designated place (CDP) in Trinity County, California. Mad River is located in the southern part of the county. Mad River sits at an elevation of 2,484 feet (757 m). The ZIP Code is 95552 and Mad River is the furthest east town in area code 707. The 2010 United States census reported Mad River's population was 420.
Mad River has the last services on California State Route 36 until the Wildwood Store, 5 miles (8.0 km) west of Platina. That is 39 miles (63 km) away. Its post office serves itself and the communities of Dinsmore (Humboldt County), and Van Duzen; both using 95552 as their ZIP code. Ruth residents with Post Office Boxes at the Ruth Store share the 95526 zip code with Bridgeville. In the Spring of 2014, Ruth residents with mail boxes on the Mad River Road are now part of the Mad River zip code and use the city designation of Mad River, CA 95552. Mad River is home to Southern Trinity High School, the region's only high school with an enrollment of 45 students. It is also home to Van Duzen Elementary School.