State Route 39 (SR 39) is a state highway in the U.S. state of California that travels through Orange and Los Angeles counties. Its southern terminus is at Pacific Coast Highway (SR 1), in Huntington Beach. SR 39's northern terminus is at Islip Saddle on Angeles Crest Highway (SR 2) in the Angeles National Forest, but its northernmost 4.5-mile (7.2 km) segment (including the connection with SR 2) has been closed to public highway traffic since 1978 due to a massive mud and rockslide.

Officially, the highway is broken into pieces. Caltrans has not adopted or signed the segment between La Habra and West Covina. Caltrans has also relinquished a portion of SR 39 in Buena Park from Stanton Avenue in Buena Park to Interstate 5 in 2013, as well as those segments within the cities of Azusa by 2010, Covina by 2010, and West Covina by 2013. Since 2001, a portion of SR 39 that runs through the city of Stanton has been considered for relinquishment to the city. If so, the portion that runs through the city of Anaheim will still be state controlled.

Major places of interest along SR 39 are Knott's Berry Farm, an amusement park; Adventure City, another amusement park targeted for children; Huntington Beach, a local beach; a Medieval Times location; the Buena Park Auto Center; and the Westridge Golf Course in La Habra.

SR 39 begins at SR 1 (Pacific Coast Highway) in Huntington Beach and runs north along Beach Boulevard to Whittier Boulevard in La Habra, with the exception of the segment between the southern city limit of Buena Park and Interstate 5, which was relinquished to the city in 2013. SR 39 then turns east along Whittier Boulevard to Harbor Boulevard, taking over a former segment of SR 72, while the remaining segment SR 72 remains on Whittier Boulevard west of Beach Boulevard.

The segment from the Whittier–Harbor intersection to the San Bernardino Freeway (Interstate 10) in West Covina is not officially designated by Caltrans (as indicated by an "END 39" sign at the Whittier–Harbor intersection). Under California Streets and Highways Code § 339 (d), the traversable route takes SR 39 along Harbor Boulevard north, Fullerton Road north, and then Colima Road west to Azusa Avenue in Hacienda Heights. SR 39 would then continue north on Azusa Avenue through the City of Industry to Interstate 10.

Adopted SR 39 then resumes and signs for SR 39 appear on Azusa Avenue from its junction with Interstate 10 in West Covina, and through Covina to First Street in the city of Azusa just north of Interstate 210. The route then runs as a couplet (composed of two one-way streets), with northbound traffic on Azusa Avenue, and southbound traffic on San Gabriel Avenue, to Sierra Madre Avenue where the two one-way streets converge to form San Gabriel Canyon Road. Although relinquished in the cities of West Covina, Covina, and Azusa, SR 39 shields remain on this segment of the highway.

State maintenance of SR 39 begins again along San Gabriel Canyon Road at the north limit of Azusa. The highway winds through the San Gabriel Mountains in the Angeles National Forest for 22.6 miles (36.4 km) until it reaches a gate barring the road 0.25 miles (0.40 km) north of Crystal Lake Road in the Crystal Lake Recreation Area. The last few miles of the route, including the connection to SR 2, are closed to public highway traffic, as the roadbed has been closed since 1978, due to major rock slides that year and again in 2005 which damaged more of the remaining roadbed.

A replacement of the section north of East Fork Road, in the next canyon to the east, was partly built in 1936 and 1961, but was never completed. The section includes one bridge and two tunnels; it was never used by automobile or truck traffic. In one local hiking guide the section is identified as the "Road to Nowhere" and the "Convict Road", although the official name is the Shoemaker Road and was planned to be an escape route in times of nuclear warfare. A ca. 1967 replacement, much closer to the existing alignment, was also stopped prematurely, and so the middle of the segment between East Fork Road and the closure gate, with its many hairpin curves, still exists.

SR 39 is part of the California Freeway and Expressway System, and the urban portions of SR 39 are part of the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration. SR 39 is eligible for the State Scenic Highway System, but it is not officially designated as a scenic highway by the California Department of Transportation.

Although defined to be a continuous route in the California Streets and Highway Code, the segment from Whittier Boulevard in La Habra to West Covina is not officially adopted or signed by Caltrans. This is indicated at the intersection of Whittier Boulevard and Harbor Boulevard, where an "END 39" sign appears.

Prior to the present before reaching Harbor Boulevard, SR 39 continued north from Whittier Boulevard along Hacienda Road to the Los Angeles/Orange County line then north on Hacienda Boulevard and Glendora Avenue to US 60, 70, and 99 (Garvey Avenue, now Interstate 10) in West Covina. It then continued east with US 60, 70, and 99 to Azusa Avenue where it turned north to follow the present alignment as described beginning in the fourth paragraph of the preceding section. The Hacienda Glendora segment can still be seen as Route 39 on some maps.

Prior to 1991, Harbor Boulevard became Fullerton Road northbound from the Los Angeles/Orange County Line, through the Puente Hills as a one-lane winding road into Rowland Heights. However, due to complaints of nearby residents due to the increased volume of traffic, a straighter, wider stub was built slightly to the east, and was named Harbor Boulevard. This route is under consideration to become part of SR 39 to complete the gap.

The new Harbor Boulevard was opened to the public early in 1992, and is now the primary corridor between Orange County and Rowland Heights, although the original winding Fullerton Road segment still exists as a strictly residential street.

The definition of Route 39 in the California Streets and Highway Code was thus changed accordingly, and the traversable route to fill the Route 39 gap would be via Harbor Boulevard north, Fullerton Road north, and then Colima Road west to Azusa Avenue in Hacienda Heights. Route 39 would then continue north on Azusa Avenue through the City of Industry to Interstate 10 in West Covina. This segment however has yet to be officially designated by Caltrans.

After the road's completion, there were frequent closures along SR 39 through the San Gabriel Valley. During the winter of 1978, following a period of heavy rainfall, a rockslide damaged the northernmost 4.5-mile (7.2 km) stretch of SR 39 near Crystal Lake to the road's terminus at SR 2, at Islip Saddle. This resulted in the permanent closure of a 6.1 mi (9.8 km) portion of SR 39. In 1990, Caltrans started maintaining the damaged sections by restoring culverts and adding berms. The transit agency offered the closed portion of the road to the United States Forest Service, which would only accept it if the road was returned to a wild state, a proposition considered to be more costly than reconstruction. During the 1997–98 El Niño event, heavy rainfall caused another rockslide that damaged sections still under construction. Following a Caltrans study, which determined that the road's reopening would not harm the environment, the closed portion was reopened as a service road and emergency route in February 2003. In June 2006, California authorized funding to conduct a three-year-long environmental impact report. It was predicted that a reopened SR 39 would reduce travel time by around 50% between Mount Waterman and Pasadena, shortening the drive from about two hours to one. According to Caltrans, work could begin in 2009 on reconstruction, as well as the installation of safety features to prevent future slides from damaging the roadway.

The environmental impact statement was completed in 2009, estimating the project's cost at $32 million (over $45 million in 2023, adjusted for inflation). After the report was released, California Fish and Wildlife informed Caltrans that the road's reconstruction would negatively affect the subspecies of bighorn sheep, the Nelson's bighorn sheep, a protected species in the state. In September 2011, Caltrans canceled plans to reopen the closed portion of SR 39. By that time, the maintenance cost for that portion of the road was $1.3 million per year. Thereafter, the agency tried to transfer responsibility for the entirety of SR 39 north of postmile LA 17.81 (including the closed section) to either the U.S. Forest Service or Los Angeles County, both of which declined for financial reasons, even though both the USFS and the county deemed the route "essential". Abandoning the route would not be cost-effective for Caltrans due to, among other reasons, federal environmental restoration requirements related to the presence of bighorn sheep. The proposal was abandoned after opposition by local residents and the county, as well as substantial legal pressure by the Forest Service, who threatened to enforce an old contract that requires Caltrans to completely deconstruct the highway should it refuse to maintain it. After lobbying from the cities of Azusa and Glendora, and support from congresswoman Grace Napolitano, Caltrans restarted plans in 2011 toward reopening the closed section of SR 39. Benefits for the project included another evacuation route for Azusa. On December 15, 2022, Caltrans held a meeting to consider several proposed plans to reopen SR 39. Proposals include a full restoration, minimal restoration for emergency services, a single-lane road, or recreational use. Under the recreational use proposal, the restored route would be closed to general traffic, but would allow for hiking, biking, and other recreational activities.

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 to an overlap due to a correction or change, and T indicates postmiles classified as temporary (for a full list of prefixes, see California postmile § Official 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.

County	Location	Postmile	Destinations	Notes
Orange ORA 0.00-17.26, 18.44-22.66	Huntington Beach	0.00	SR 1 (Pacific Coast Highway) – Long Beach, Newport Beach	Southern terminus; former US 101 Alt.
	Huntington Beach–Westminster line	5.80	I-405 (San Diego Freeway) – Long Beach, Irvine, San Diego	I-405 exit 16; former SR 7
	Westminster	8.48	SR 22 (Garden Grove Freeway) – Long Beach, Santa Ana, Orange	SR 22 exit 8
	Anaheim	12.71	Lincoln Avenue	Former SR 214
	Anaheim–Buena Park line	12.91	Stanton Avenue	North end of state maintenance
	Buena Park	14.38	SR 91 (Artesia Freeway) – Riverside, Artesia, Beach Cities	SR 91 exit 23B
		15.07	I-5 (Santa Ana Freeway) – Los Angeles, Santa Ana, San Diego	Interchange; south end of state maintenance; I-5 exit 116; access to and from northbound I-5 via Auto Center Drive
		15.08	Auto Center Drive	Formerly Manchester Avenue and former SR 10
		15.57	To I-5 north / Artesia Boulevard	Alternate southbound access to I-5 north via Artesia Boulevard west
		15.63	Stage Road / Cascade Way	Stage Road was formerly SR 26
		16.38	La Mirada Boulevard (CR N8) / Malvern Avenue	Southern terminus of Los Angeles County Route N8
	La Habra	19.17	SR 90 east (Imperial Highway) – Brea, Yorba Linda	Western terminus of SR 90; Imperial Highway was former SR 90 west before being relinquished to local jurisdictions
		20.72	SR 72 north (Whittier Boulevard) – Whittier	Former US 101; Whittier Boulevard was former SR 72 south before being relinquished to local jurisdictions
		22.66 0	Whittier Boulevard east / Harbor Boulevard south	North end of Orange County segment, as adopted and signed by Caltrans; former US 101 south; former SR 72 south
Los Angeles LA 10.70-44.40	Rowland Heights	4.0	Fullerton Road north / Colima Road east
	Hacienda Heights–City of Industry line	5.5	Colima Road west ( CR N8) / Azusa Avenue south	South end of CR N8 overlap
	City of Industry	5.9	SR 60 (Pomona Freeway) – Los Angeles, Pomona	SR 60 exit 18
		6.8	Chestnut Street	Interchange; northbound exit and entrance only
		6.9	Valley Boulevard	Interchange; access via connector roads
	South San Jose Hills–Valinda– West Covina tripoint	8.1	Temple Avenue	North end of state control, as defined by Streets and Highways Code § 339 (d)
	West Covina	11.5 10.71	CR N8 ends	South end of Los Angeles County segment, as adopted and signed by Caltrans;; north end of CR N8 overlap; I-10 exit 36; former US 99
			I-10 (San Bernardino Freeway) – Los Angeles, San Bernardino
	Azusa	14.05	I-210 (Foothill Freeway) – Pasadena, San Bernardino	I-210 exit 40
		17.81	Bridge over San Gabriel River South end of state maintenance
	​	39.90	Northbound road closure gate
	Islip Saddle	44.40	SR 2 (Angeles Crest Highway) – La Cañada Flintridge, Wrightwood	Closed; northern terminus
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Closed/former       Incomplete access

• California Roads portal

• Caltrans: State Route 39 highway conditions
• Caltrans Traffic Conditions Map
• California Highway Patrol Traffic Incidents
• California @ AARoads.com - State Route 39
• California Highways: SR 39
• Michael Ballard on SR 39
• SR 39 EIR