The Mountain Quarries Bridge is located approximately a mile east of the City of Auburn across the American River, just downstream from the confluence of its north and middle forks, and immediately downstream from the State Route Highway 49 crossing. Although massive, the arch bridge is plain in appearance yet possesses a gracefulness that is in perfect harmony with its rugged surroundings.

In 1910 the newly formed Mountain Quarries Company of San Francisco, a subsidiary of Pacific Portland Cement Company, contracted the Duncanson-Harrelson Company to construct a railroad bridge to cross the American River just below the confluence of the North Fork and the Middle Fork, near their limestone quarry. The bridge was a single-track structure used for a standard gauge rail, 482 feet from abutment to abutment. The Placer County approach is 72 feet in length, while the El Dorado County approach is 100 feet long, making the overall length of the structure about 650 feet. The bridge is 15 feet wide and 70 feet high with three 140-foot solid barrel skewed arch spans. At the time of its construction in 1911 the span bore the distinction of being the longest span concrete arch railroad bridge owned by a private concern. The heavy Mallet compound engine used by the company along with the weight being carried behind it required the bridge to be carefully designed. It continued to serve as a railroad bridge until about 1940 after which it was used as an equestrian crossing.

300 men at a cost of $300,000 completed the bridge in two years.

In the early 1900's the Pacific Portland Cement Company built a special railroad line that connected their limestone quarry operation known as Mountain Quarry in El Dorado County four miles east of Auburn, California, along the Middle and North Forks of the American River, near Junction Bar, with the west bound Southern Pacific main line at Auburn, in Placer County. The high grade of limestone was quarried and transported by rail for use in the manufacturing of cement and the refining of sugar.

The Mountain Quarry Cement Bridge or Mountain Quarries Bridge, sometimes referred to as "No Hands Bridge", was completed on March 23rd, 1912. At the time of its construction the bridge was the longest concrete skew arch railroad bridge in the world. The building of the bridge was also to determine if concrete was practical in building long bridges. Although a couple of construction faults plagued the building of the Bridge it was considered a great piece of railroad bridge engineering. The bridge stands today as a proud monument to early day engineering and to the men who worked with somewhat primitive tools to create it.

The Mountain Quarries Bridge has withstood the tugging of the American River currents for over 90 years and stayed on its footings when the Hell Hole Dam broke in December of 1964 and took out two modern bridges upstream. The Bridge also withstood the so-called "Valentine Day Flood of 1986" which caused the destruction of a 200-foot earth-filled coffer dam a few miles further down river. These and other occurrences attest to the achievement of John Leonard's use of reinforced concrete.

Today part of the former railroad route is part the Western States Pioneer Express Recreation Trail and the bridge is open to equestrians, cyclist, and pedestrians. It is the final the final American River crossing of the Western States Hundred Mile Endurance Ride and Run.