John C. Hawver, an amateur geologist, discovered a limestone cave near Cool around 1900. Archeologists from UC Berkeley explored the cave in 1907, and found prehistoric bones and the tusks from a mastodon. 

Mountain Quarries Company later mined this limestone deposit for cement and processing sugar beets. At peak production, the plant employed 150-200 men—who would work two, eight-hour shifts—and produced 1,000-1,500 tons of limestone per day. 

The seven-mile-long standard gauge Mountain Quarries Railroad and the Mountain Quarries Bridge were located on the Middle Fork of the American River in El Dorado County east of Auburn. Both were built simultaneously beginning in 1910. Over 1,000 men were employed in this effort at a cost of close to a million dollars, which would be $25 million today.

George Herrington, an engineer with the Southern Pacific Railroad, was in charge of construction on the Mountain Quarries Railroad. Palmer, McBride, and Quail was the contractor with approximately 600 men working on the project, which began in Placer County and ended across the river in El Dorado County. Lumber for the 17 trestles and the scaffolding used to construct the bridge were supplied by Auburn Lumber Company. 

 The Mountain Quarries Bridge—designed by John Leonard and built by Duncanson and Harrelson Company—still stands at the confluence of the Middle and North Forks of the American River. 

Concrete bases—which are actually hollow boxes with 18-inch-thick concrete walls reinforced with one-and-a-half-inch twisted steel bars and filled with uncrushed rock—sit on top of bedrock at the bottom of the river and support the piers. The arches are also hollow and filled with crushed limestone. The railbed was filled with sand and topped with limestone.

On November 4, 1911, as crews worked late into the night, calamity struck. According to a contemporary account, “the third arch was being poured…when some of the underpinning let go and the whole of the arch came down with 20 men on it—three were killed, five injured, the others escaping with scratches.” The wooden scaffolding had collapsed under the weight of the wet cement. A coroner’s inquest found no one at fault for the deaths.

The Mountain Quarries Bridge was completed on March 23, 1912. It has three, 140-foot-long arches and is 482 feet long with the railroad bed 15 feet wide and 80 feet above low water. At the time, it was reputed to be the “longest span concrete arched bridge for railroad traffic owned by private capitol” in the world. It was built at a cost of $300,000—or the equivalent of $7.5 million today.

In July 1912, Pacific Portland Cement Company purchased Mountain Quarries Company, the railroad, and rolling stock. The railroad operated until 1941; in 1942, the tracks were taken up for war scrap during WWII.  

On December 23, 1964, the failure of the Hell Hole Dam upriver sent 30,000 acre-foot of water down river, which destroyed the Highway 49 Bridge. The Mountain Quarries Bridge withstood the flood and was used for vehicular traffic during the 107 days it took to rebuild the bridge.

Dubbed the No Hands Bridge, the concrete marvel was closed in 1996 due to the erosion of its southern pier. Congressman John Doolittle authored the No Hands Bridge Restoration Act of 1997 to provide $700,000 for repairs. Private citizens also raised over $50,000. In July 1998, the Bureau of Reclamation awarded a $650,000 contract for repairs to American Pacific Marine of Oxnard.

Much of the Mountain Quarries railbed is now part of the trail system in Auburn State Recreation Area; in 2014, the bridge was designated a California Historical Landmark.