Lonely Are The Brave (1962)

Jack Burns (Kirk Douglas), a roaming cowboy whose fierce individualism is at odds with contemporary urban values, emerges from the mountains when he learns that his friend Paul Bondi (Michael Kane) has been jailed for helping illegal immigrants cross the border into the United States. Deliberately jeopardizing his own freedom to join his old pal Bondi behind bars, Burns is greeted by a virtual stranger. Bondi's tamed spirit and conventional outlook force Burns to address the very real mortality of his old-fashioned idealism. Burns makes a break for the border on his beloved horse Whisky, determined to preserve his chosen lifestyle.

IMDb: https://www.imdb.com/title/tt0056195