State Route 175 is a state highway in California, USA.

CA Route 175 connects U.S. Route 101 at Hopland to State Route 29 near Lakeport through the Mayacamas Mountains. From there it joins Route 29 until Kelseyville, where it loops out until meeting Route 29 again at its end at Middletown. The section between Hopland and Lakeport is also known locally as the "Hopland Grade", or "Hopland Pass."

Originally constructed in the early 1920s, it is one of the steepest and most difficult to drive of any California state highway. Indeed, until recently it was called the "crookedest road in California". Vehicles more than 39 feet (12 m) in length are banned from the Hopland Grade, due to its many tight hairpin turns and curves.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.