The second transcontinental railroad was the product of two railroad companies, same as the first transcontinental. The Southern Pacific built eastward from the Pacific Ocean (starting from their line in El Paso, TX in 1881), while the Galveston, Harrisburg & San Antonio Railroad built west from the Gulf of Mexico (from their terminal at San Antonio, TX in 1880). The two groups met in 1883 about three miles west of the Pecos River, driving a silver spike to commemorate the occasion of being the first railroad to stretch from the West Coast to the Gulf Coast.
The Pecos River was a formidable barrier. For 60 miles from its mouth at the Rio Grande, the Pecos is within a canyon that is over 300 feet deep and over 1,500 feet across. In 1880-1882, it was technical infeasible for the GH&SA to cross such an obstacle, so the route chosen went along the northern bank of the Rio Grande and crossed the mouth of the Pecos River in more traditional style of trestles and a thru-truss bridge. This route also required two tunnels (one is about 1,500 feet long; the other one is about 1,400 feet long and can be seen at 29°44'9.93"N 101°23'47.06"W.) However, flooding caused the route to be unreliable and the route was frequently inundated or damaged by erosion. A different route had to be considered.
A second route was defined that would cross the Pecos River about 5 1/2 miles upstream of the original crossing. The grades could be a bit flatter (1.8% on average vs. 2% on average) and the new route was half the distance of the 26 mile original route from tie in to tie in. This route and the second Pecos High Bridge was completed in 1892 under Southern Pacific. The old route with its numerous cuts and fills remains, but the route, trestles, and bridges are all gone.
The abandoned routes for both the first and second High Pecos Bridges are mapped.