From the National Park Service article on Navajo Bridge:
Those traveling across the country on Highway 89A between Bitter Springs and Jacob Lake, AZ arrive at two bridges similar in appearance spanning the Colorado River.
These two bridges, one historic and one new, represent one of only seven land crossings of the Colorado River for 750 miles (1207 km).
Five highway bridges and two trail bridges in the Grand Canyon are the
only seven land crossings of the Colorado for 750 Miles (NPS).
There were no bridges across the Colorado between Moab, Utah, and Needles, California, a distance of 800+ miles, a barrier dividing the northwest and southwest, until the historic Navajo Bridge opened in 1929.
History of Bridges extends this by nearly 100 miles with information on the Fruita, Colorado, and Dewey, Utah, bridges to the east, and the Topoc, Arizona/Needles, California, bridges at the southwestern end, with history, dates, and mileages for all the bridges.
Scenic views of the bridges cycle in the banner above, in the order in which they appear, southwest across Utah and Arizona.
At Moab, Utah, amidst unique geology, the US191 Colorado River Bridge is designed to be in harmony with nature. The Bridge at Hite Crossing on Utah Scenic Byway 95 and the Trail of the Ancients near Hite, Utah, is 110 miles (177 km) downstream, crossing the Colorado over Cataract Canyon and the northeastern end of Lake Powell. The US89 Glen Canyon Dam Bridge crosses the Colorado at the southwestern end of Lake Powell near Page, Arizona, is 185 miles (298 km) downstream. Historic Navajo Bridge on US89A over the Colorado in Marble Canyon is 15 miles downstream. The South Kaibab Trail and Bright Angel Trail bridges cross the Colorado near the floor of the Grand Canyon. The Mike O'Callaghan-Pat Tillman Memorial Bridge, the US93 Hoover Dam Bypass, is an amazing structure with a pedestrian walkway providing a view of Hoover Dam and the Colorado 900' (280+ m) below in Black Canyon.
The road looked as if it had been cut out of the red clay mountains with a pocket knife wrote Sharlot Hall about her trip down the side of the canyon to Lee's Ferry in 1911.
More information may be found in the Navajo Bridge History article.
In 1987, casino owner Don Laughlin built a bridge across the Colorado between Laughlin, Nevada, and Bullhead City, Arizona, at a cost of $3.5 million, to provide Arizona-access to his casino.
He donated the bridge to the states of Nevada and Arizona.
The 26 miles between Laughlin and Needles partially explains the difference between the 800+ between Moab and Needles, and 750 miles between bridges, as quoted above.
Photos are in the gallery.A pre-bridge Colorado River crossing was the unsafe Lee's Ferry, near the present location of Navajo Bridge in Marble Canyon, that operated between 1871 and its destruction in an accident in 1928 (Navajo Bridge was being constructed at the time of the accident, opened in 1929).
A ferry operated by Arthur Chaffin crossed the river at Hite Crossing from 1946 until 1966 when the Bridge at Hite Crossing was built as Lake Powell started filling after the Glen Canyon Dam was built.
And a new bridge was built in 1987 by Don Laughlin at Laughlin, Nevada, a few miles upstream from Needles.
Cycling photos at about 7 second intervals, with obscure previous/pause-resume/next/stop image-buttons in the upper-right corner that will light up on mouse-over. Select pause and previous/next to view at different interval or highlight information, resume to continue with the next photo. The Photo Gallery contains photos of the seven bridges and the three bridges discussed in History of Bridges (Fruita, Dewey, US66 at Topoc/Needles). Select a bridge from the Bridges Menu to open a page with its story and an auto-show of its photos. Quick Tour is an auto-show with one photo of each bridge including the historical bridges. All Bridge Photos is an auto-show of all of the Colorado River bridges photos in the photo gallery. Landslide provides details and videos from the Arizona Department of Transportation of the Feb. 20, 2013, event that closed US89 for 25 months.