Mounting his hammerhead roan, [Chick] Bowdrie let the long-legged horse turn back up the arroyo trail. The roan took his own pace, a shambling loose-limbed trot, and the miles began to fall behind.
The Collected Short Stories of Louis L’Amour, Volume 2, Frontier Stories.

Chick Bowdrie, with his dark Apache-like face, and his hammerhead roan horse, ready to bite if you came at him from the wrong direction, were a good pair. Each could be stubborn and happiest on the trail, always ready to get the job done, no matter how long or difficult.
For the most part, this well-matched pair rode along the trail of Texas and the southwest in silence. I have come across only one instance where Bowdrie spoke to his companion, “What I want to know Hammerhead, is how the fifth bandit got away. More than likely, if he rode around behind the Rest and took to the woods, he had to come this way to keep from sight. He had to know a trail leading him up to the breaks of the plateau without using the main trail.” Bowdrie by Louis L’Amour.