Complex sentence: According to Ed Lemmon in "Boss Cowman," he hung around end-of-the-Texas-Trail Ogallala, Nebraska, in late 1877 and the first half of 1878 gambling at Cowboy's Rest Saloon, sometimes in the company of Bat Masterson.
Split into simpler sentences: According to Ed Lemmon in "Boss Cowman," he was in Ogallala, Nebraska, the northern point of the Texas Trail, from 1877 to 1878. During this time, he gambled at Cowboy's Rest Saloon, sometimes in the company of Bat Masterson.