Construction began on July 1, 1928, with convict labor for the easier portions and contractors for the remainder, as well as bridges and tunnels, but was slowed by the Great Depression. On the most difficult portion, between Cresta and Rock Creek, three tunnels had to be built at Arch Rock, Grizzly Dome, and Elephant Butte; at the former two, surveyors had to hang out on rope over steep granite slopes, and rockslides repeatedly caused delays. The commission dedicated the road at a ceremony at Grizzly Dome, halfway between the ends, on August 14, 1937. Construction had cost $8.15 million for 78 miles (126 km) of new road. The remainder of the old trail from Quincy to the junction with Route 29 (now U.S. 395) east of Beckwourth Pass was added to the state highway system in 1931 as an extension of Route 21, and was paved by 1936. A new Route 87 was created in 1933, stretching from Woodland via Marysville and Oroville to Route 3 (State Route 99) southeast of Chico, including the present SR 70 between Marysville and Oroville. Route 87 from Woodland to Oroville and Route 21 from Oroville to east of Beckwourth Pass became a new State Route 24 in 1934; State Route 24 was extended southwest from Woodland to Oakland by the end of 1937.