In an early pivotal scene, the men in charge of the Union Pacific and the Central Pacific Railroads meet in Salt Lake City with Ulysses Grant to discuss the route each railroad will take and whether or not the terminus of each railroad will be Salt Lake City. Nearly each man sitting at the table with Grant refers to him as "Mr. President" or "President Grant". There is a newspaper used as a prop and it is dated Friday May 29, 1868. Ulysses Grant was not elected President until November 3, 1868 and his inauguration was not until March 4, 1869. So this is an historically inaccurate scene because Grant was addressed as "Mr. President" even though this particular scene took place almost 6 months before Grant was elected and about 9 months before his inauguration of March 1869. Andrew Johnson would have still been President on May 29, 1868.
Cullen refers to the "Utah state line," but Utah didn't become a state until 1896, almost 30 years after the setting of the show.