sentences:  The Rock Island was one of several railroads competing in the Chicago–Denver passenger market.The Chicago, Burlington and Quincy Railroad started the streamliner era in the United States in 1934 when its "Pioneer Zephyr" made its special "Dawn-to-Dusk" run from Denver to Chicago in 13 hours 5 minutes.By 1936 both the Burlington's "Denver Zephyr" and the Union Pacific Railroad's "City of Denver" were locked in head-to-head competition, each with new equipment and a 16-hour schedule.