The best book to answer your question is "The North American Railroad: Its Origin, Evolution and Geography" by James Vance jr. (1995) The second chapter of this book "The drive for ubiquity: The Middle Western Railroad" details the four major surveys, conducted by the Army Corps of Engineers after the Pacific Railroad Act of 1854 authorized a systematic look for the best route for a railroad to the Pacific.
The 32nd Parallel route was not surveyed, since the Army gained considerable geographic knowledge of that area in their recent war with Mexico. They also knew the best pass over the Rocky mountains lay to the south of the recently redrawn border with Mexico and that fact led to the Gadsen Purchase of 1853. Since Jefferson Davis was the strongest proponent of that route, Northern states refused to fund such a southern route to the Pacific, despite the fact it was the shortest and easiest route.
The 35th parallel route was investigated by Lieutenant A.W. Whipple, from Fort Smith Arkansas to Los Angeles California. This route eventually was built by the Santa Fe railroad during the 1880s.
The 38th parallel route was under the command of Lieutenant John Gunnison. This route was chosen because Senator Benton of Missouri, who never went west of Fort Levenworth Kansas himself, was convinced that Cochetopa Pass in southern Colorado, was the geographical key to the building of a transcontinental railroad. While Cochetopa Pass was indeed the lowest crossing of the Rocky Mountains in the state of Colorado, the path west from there is blocked by the Sangre de Christo mountain range and difficult hill country west of that mountain range until they encountered the Grand Canyon. They survey stopped there and did not even make it to Nevada, let alone the Pacific coast.
The Army did not conduct a complete survey along the 41st parallel route. The eastern half was well known as the Oregon Trail and Lieutenant Beckwith was able to find a good route for a railroad through the Wasatch mountains, east of the Great Salt Lake Basin, in Utah.
The 47th and 49th Parallel route surveyed the path between the Puget sound and Saint Paul Minnesota. Under the command of Lieutenant Isaac Stevens, it was the first group to start their survey. There are five major mountain ranges in Montana. To take advantage of the river valleys that cut through these mountains, the route zigzags much more so than the three surveys conducted further to the south. This route was eventually built by the Northern Pacific railroad, during the 1880s. They missed Marias pass completely, which was still deep inside the land controlled by the Blackfeet Indian nation during the 1850s.
The Vance book has a listing of the primary source documents, written by Howard Stansbury, Isaac Stevens, E.G. Beckwith, Frederick Lander and A.W. Whipple. These War Department government reports were printed between 1854 and 1856 and all have paragraph long titles. None of them are illustrated with photos or paintings, but they do have maps.
A more recent book is "The Classic Western American Railroad Routes" edited by Bruce Clement Cooper (2010). This book does not have the academic heft of the James Vance book, but it is lavishly illustrated with 19th century photographs, paintings and old railroad company literature. It also has long essays by noted railroad historians, like William D Middleton and Brian Solomon. It covers four of the transcontinental routes rather well, but it ignores the last three routes that were built, the Great Northern, the Milwaukee Road and the Western Pacific.