In Riverside County, the highway runs through the cities of Temecula, Murrieta, Hemet, and San Jacinto before reaching Beaumont.

This portion of the route is very serpentine, with hairpin turns, as it follows the contours of the land by moving laterally, rather than up-and-down or via cuts.

[9] A stage road went through Oak Grove, and stagecoaches ran from 1858 to 1861 on a route from San Francisco to St. Louis and Memphis.

[11] A railroad line to Cuyamaca was under construction by 1887,[12] though in 1889 the project encountered problems from workers departing to work in the nearby gold mines.

[18] However, the next year, the county highway commissioners determined that more funding would be needed to complete the road to Warner Springs.

[19] By November 1912, the road to Warner Springs from San Diego was completed, including the part from Santa Ysabel, which had been widened.

[20] The road south of Julian to Decanso was open by 1916, but had a narrow crossing at the Cuyamaca dam, making the trip difficult.

[25] The next year, plans were presented to realign part of the road between Julian and Cuyamaca, including one proposal to have it cross the lake.

[26] The California Chamber of Commerce made the suggestion in 1962 to convert SR 79 from Descanso to Julian to be an expressway.

Following the Cedar Fire in October 2003, utility poles and wires fell down on the highway, and the Cuyamaca area was heavily damaged.

[34] Due to increased traffic congestion through the San Jacinto Valley, there are plans to realign SR 79 to a new four-lane (eventually six-lane)[35] limited-access expressway, spanning approximately 12 miles from East Newport Road to the southern end of the current divided highway portion at Ramona Expressway.

[37] 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.