Wikipedia:WikiProject U.S. Roads/California/History/Joint Highway Districts

[1] has a list.

• Joint Highway District No. 1: Skyline Boulevard, San Francisco, Santa Clara, San Mateo, and Santa Cruz Counties, March 22, 1919
  • added 1919 as SR 55 (1933 in SF)
• Joint Highway District No. 2: Cuyama Road, Santa Maria to Bakersfield, Santa Barbara, Kern, and San Luis Obispo Counties, May 20, 1919 (also listed as "Huasna-Alamo Bridge" - huh?)
  • added 1919 as SR 57
• Joint Highway District No. 3: Garden Highway (13 mile gap), Sacramento and Sutter Counties, December 15, 1922
  • added either 1949 as SR 207 (232) or 1959 as SR 245, depending on where the gap was
• Joint Highway District No. 4: Rio Vista to Antioch, Contra Costa and Sacramento Counties, November 18, 1925
  • added 1933 as SR 11
• Joint Highway District No. 5: Carquinez Bridge north approach, Napa and Solano Counties, October 14, 1926
  • added 1931 as SR 74
• Joint Highway District No. 6: Maricopa-Ventura-Carpinteria Highway, Kern, Ventura, and Santa Barbara Counties, October 28, 1926; formally opened October 22, 1933
  • added 1933 as SR 138 (and SR 151??)
• Joint Highway District No. 7: Geyser Highway, St. Helena? Calistoga? to Healdsburg, Napa and Sonoma Counties, February 23, 1927
  • added 1933 as SR 103 (and SR 49??)
• Joint Highway District No. 8: Sears Point Cutoff, Marin and Solano Counties, September 8, 1927
  • added 1939 as SR 208
• Joint Highway District No. 9: SR 1 from Santa Cruz to San Francisco, San Francisco, San Mateo, and Santa Cruz Counties, May 28, 1928
  • "This joint highway district was organized May 28, 1928 to provide for the improvement of the Ocean Shore Highway in Santa Cruz, San Mateo and San Francisco Counties. During the 1931 Session of the Legislature this route was taken into the State Highway System as State Highway 56, or as it is known to the traveling public, State Sign Route 1."
  • added 1933 as SR 56 (despite the above quote)
• Joint Highway District No. 10: Junipero Serra Boulevard, San Francisco and San Mateo Counties, September 15, 1928
  • "This joint highway district was organized September 15, 1928, by San Francisco and San Mateo Counties. It is now planned to cover construction of Junipero Serra Boulevard Extension, between San Francisco and Millbrae Avenue in the City of Millbrae, San Mateo County. No state highways are included in this district."
  • added 1956 as SR 237
• Joint Highway District No. 11: Weed-Klamath Falls Highway, Siskiyou, Shasta, and Tehama Counties, October 16, 1928
  • added 1931 as SR 72
• Joint Highway District No. 12: Sutter Basin Road, Knights Landing to Tudor, Yolo and Sutter Counties, July 5, 1929
  • added 1933 as SR 87
• Joint Highway District No. 13: Broadway Tunnel, Alameda and Contra Costa Counties, July 22, 1929
  • added 1931 as SR 75
• Joint Highway District No. 14: Susanville to Oregon, Lassen and Modoc Counties, December 21, 1929
  • "This joint highway district was organized December 21, 1929 by Lassen and Modoc Counties. The district originally was comprised of the Susanville-Adin county road and portions each of State Highway Routes 28 and 210 between Adin and the Oregon Line at Tule Lake."
  • added 1943 as SR 210 and 1959 as SR 20/216
• Joint Highway District No. 15: Ortega Highway, San Juan Capistrano to Elsinore, Riverside and Orange Counties, March 26, 1930
  • added 1933 as SR 64
• Joint Highway District No. 16: Sausalito to Fernbridge? including the Jenner Bridge, San Francisco, Marin, Sonoma, Mendocino, and Humboldt? Counties, August 23, 1930
  • added 1933 and 1951 as SR 56
• Joint Highway District No. 17: Julian to Kane Springs, San Diego and Imperial Counties, October 22, 1930
  • added 1933 as SR 198
• Joint Highway District No. 18: Proberta to Los Molinos, Butte and Tehama Counties, March 13, 1931
  • never became a state highway
• Joint Highway District No. 19: Cotati to Guerneville and Healdsburg to Jenner, Mendocino and Sonoma Counties, October 5, 1931
  • added 1933 as SR 104 (Healdsburg to Guerneville never became a state highway)
• Joint Highway District No. 20: Vina to Longvale, Mendocino and Tehama Counties, December 4, 1931
  • partly added 1965 as SR 261; remainder never became a state highway
• Joint Highway District No. 21: Lassen Park to Pacific Highway, Shasta and Trinity Counties, December 14, 1931
  • added 1933 as SR 20
• Joint Highway District No. 22: Red Bluff to Redwood Highway, Tehama, Trinity, and Humboldt Counties, June 10, 1932
  • added 1933 as SR 29 and SR 35
• Joint Highway District No. 23: Willits to Noyo, Leggett Valley to Rockport to Russian Gulch, and Navarro River to Gualala River, Mendocino and Sonoma Counties, August 12, 1932
  • added 1933 and 1951 as SR 56 and 1953 as SR 15
• Joint Highway District No. 24: Yuba Pass Extension, Marysville to Downieville, Sierra and Yuba Counties, November 20, 1936
  • never became a state highway?
• Joint Highway District No. 25: Sausalito to Golden Gate Bridge, Marin, Sonoma, and Napa Counties, June 30, 1937
  • added 1937? as SR 1
• Joint Highway District No. 26: Warren Boulevard, Oakland to San Leandro, Alameda and Contra Costa Counties, September 26, 1938-1954
  • added 1947 as SR 227
• Joint Highway District No. 27: Lucerne Cutoff Road, Route 20 to Route 29, Lake and Mendocino Counties, June 11, 1942
  • never became a state highway