In competition with the Santa Fe Chiefs, the Rock Island jointly operated the Golden State Limited (Chicago—Kansas City—Tucumcari—El Paso—Los Angeles) with the Southern Pacific Railroad (SP) from 1902 to 1968. On this route, the Rock Island's train was marketed as a "low-altitude" crossing of the Continental Divide. The Rock Island did not concede to the Santa Fe's dominance in the Chicago–Los Angeles travel market and re-equipped the train with new streamlined equipment in 1948. At the same time, the Limited was dropped from the train's name and the train was thereafter known as the Golden State. The local run on this line was known as the Imperial, which had a branch operating through the northwestern edge of Mexico.

The 1948 modernization of the Golden State occurred with some controversy. In 1947, both the Rock Island and Southern Pacific jointly advertised the coming of a new entry in the Chicago-Los Angeles travel market. The Golden Rocket was scheduled to closely match the Santa Fe's transit time end-to-end and was to have its own dedicated trainsets, one purchased by the Rock Island, the other by Southern Pacific. As the Rock Island's set of streamlined passenger cars was being finished, the Southern Pacific abruptly withdrew its purchase. The Rock Island's cars were delivered and found their way into the Golden State's fleet soon after delivery.

The Golden State was the last first-class train on the Rock Island, retaining its dining cars and sleeping cars until its last run on February 21, 1968.

The Rock Island also competed with the Chicago, Burlington and Quincy railroad in the Chicago-to-Denver market. While the Q fielded its Zephyrs on the route, the Rock Island ran the Rocky Mountain Rocket. The RMR split at Limon, Colorado, with half the train diverting to Colorado Springs, an operation known as the "Limon Shuffle". The Rock Island conceded nothing to its rival, even installing ABS signaling on the route west of Lincoln in an effort to maintain transit speed. The train was also re-equipped with streamlined equipment in 1948.

As the Rocky Mountain Rocket was downgraded due to nonrail competition, the route traveled by the train was gradually shortened from 1966 onward. Its western terminus was cut back first to Omaha, then to Council Bluffs. After briefly running without a name, it was renamed The Cornhusker. Finally, in 1970, the train was cut back to a Chicago-Rock Island run entirely within the confines of the state of Illinois and renamed the Quad Cities Rocket.

Other trains operated by the Rock Island as part of its Rocket fleet included the Corn Belt Rocket (Chicago—Des Moines—Omaha), the Des Moines-Omaha Limited (Chicago-Des Moines-Omaha), the Twin Star Rocket (Minneapolis—St. Paul—Des Moines—Kansas City—Oklahoma City—Fort Worth—Dallas—Houston), the Zephyr Rocket (Minneapolis—St. Paul—Burlington—St. Louis), the Choctaw Rocket (Memphis—Little Rock—Oklahoma City—Amarillo) and the Cherokee (a local counterpart to the Choctaw Rocket, Memphis-Little Rock-Oklahoma City-Amarillo-Tucumcari-Los Angeles).