Son Of An Arizona Legend by Stephen Bly (Stuart Brannon Series, Book 6) from Books In Motion.com

Stuart Brannon's fortieth Birthday party turns into a real surprise with the arrival of an unexpected guest--a twelve year-old son he never knew he had! The boy also brings sad news that his mother, whom Brannon had befriended at Broken Arrow Crossing, is now dying in a Navajo camp. Brannon determines to bring her back to his ranch, but chooses to wait and see her with the boy before telling Littlefoot the truth of his outlaw parentage. Danger stalks the trail to the Utah border. A desperado Brannon once sent to prison is closing in on him, determined to have revenge. A gun battle breaks out, and Brannon captures the man again. Then the outlaw tricks a gullible sheriff into locking up Brannon instead. Brannon is pitted against the shrewdest outlaw of his career, and again faces another crucial question.