California State Route 175
|Defined by Streets and Highways Code § 475|
|Maintained by Caltrans|
|Length:||37.89 mi (60.98 km)|
|Restrictions:||No vehicles more than 39 feet (12 m) in length between Hopland and Lakeport|
|West end:||US 101 at Hopland|
|SR 29 near Lakeport|
|East end:||SR 29 at Middletown|
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, based on the alignment that existed at the time, and do not necessarily reflect current mileage. R reflects a realignment in the route since then, M indicates a second realignment, L refers an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see the list of postmile definitions). Segments that remain unconstructed or have been relinquished to local control may be omitted. The numbers reset at county lines; the start and end postmiles in each county are given in the county column.
|Hopland||0.00||US 101 – Ukiah, Santa Rosa||West end of SR 175|
|SR 29 north / South Main Street – Lakeport||West end of SR 29 overlap|
|SR 29 south – Lower Lake||East end of SR 29 overlap|
|Middletown||28.04||SR 29 (Calistoga Road) / Main Street – Lower Lake, Calistoga||East end of SR 175|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi
- Indicates that the postmile represents the distance along SR 29 rather than SR 175.
- "Special Route Restriction History - Route 175". Caltrans. Retrieved 2014-07-25.
- January 1, 2006 California Log of Bridges on State Highways
- Staff. "State Truck Route List" (XLS file). California Department of Transportation. Retrieved March 1, 2015.
- California Department of Transportation, Log of Bridges on State Highways, July 2007
- California Department of Transportation, All Traffic Volumes on CSHS, 2005 and 2006