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 until it reaches a gate barring the road 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. Although Google Maps and other mapping services may list this section of the road as an "available" route to connect to SR 2, this section actually remains closed. 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