Dam Good Luck: From the beginning, Las Vegas was built to serve travelers. The railroad needed a way station, and Las Vegas was the place. Growth continued for ten years, and by 1915 the town had telephones, round-the-clock electricity, and a growing population — many of whom worked in the railroad repair shop. But such heady progress would soon come to a halt. The growing competition in rail transport resulted in Union Pacific buying the Los Angeles–Salt Lake line. Union Pacific then consolidated its operations, eliminating the Las Vegas repair facility. Additionally, Las Vegas had been made a part of Nevada's new Clark County in 1909, a year when the legislature also outlawed gambling. These unfortunate circumstances threatened to relegate Las Vegas to the status of a small desert community that could no longer support its 3000 residents. But the southwest's growing need for water, combined with Las Vegas's fortuitous proximity to the Colorado River, would give Las Vegas a second chance to achieve prosperity. Construction on Hoover Dam (originally Boulder Dam, subsequently renamed for the president who authorized the project) began in 1931 in a canyon 45 miles (72 km) southeast of Las Vegas. Providing an influx of $165 million to the southwestern economy, Hoover Dam played a major role in preventing Las Vegas from drying up, both financially and literally. Not only did it create jobs, but it also created Lake Mead, the massive reservoir that today provides water to all of southern Nevada. More Government Help: The construction of Hoover Dam did not single-handedly save Las Vegas, however. The state legislature helped as well, by legalizing gambling in 1931 and thus solidifying the future of the town, though legislators and residents could never have known this at the time. The hordes of people who attended Hoover Dam's 1935 dedication set the city's now-formidable public relations machine into action. They went to work on what has become one of the lengthiest citywide tourism campaigns ever attempted. It didn't take long for the city to establish itself as a wild-West town with an "anything goes" attitude. Vices outlawed or heavily controlled elsewhere were legal here, available any hour of any day (or night). 
What happened to the operations after Union Pacific purchased the Los Angeles-Salt Lake line?
They came together