Sanborn also offered to trade lots in the new location to businesses in the original city�s site and help with the expense of moving to new buildings. His incentives gradually won over people, who moved their businesses to Polk Street in the new commercial district. Heavy rains almost flooded Berry�s part of the town in 1889, prompting more people to move to Sanborn's location. This eventually led to another county seat election making Sanborn's town the new county seat in 1893.
By the late 1890s, Amarillo had emerged as one of the world's busiest cattle shipping points, and its population grew significantly. The city became an grain elevator, milling, and feed-manufacturing center after an increase in production of wheat and small grains during the early 1900s. Discovery of gas in 1918 and oil three years later brought oil and gas companies to the Amarillo area. The United States government bought the Cliffside Gas Field with high helium content in 1927 and the Federal Bureau of Mines began operating the Amarillo Helium plant two years later. The plant would be the sole producer of commercial helium in the world for a number of years. The U.S. National Helium Reserve is stored in the Bush Dome Reservoir at the Cliffside facility.
Following the lead of the Fort Worth and Denver City Railroad, the Atchison, Topeka and Santa Fe Railway and Chicago, Rock Island and Pacific Railroad established services to and from Amarillo. Each of these three carriers maintained substantial freight and passenger depots and repair facilities in the city through most of the 20th century and were major employers within the community.
In 1929, Ernest O. Thompson, a decorated World War I general and a major businessman in Amarillo, was elected mayor to succeed Lee Bivins. Thompson instituted a major capital improvements project and worked to reduce utility rates. He joined the Texas Railroad Commission by appointment in 1933 and was elected to full terms in
