I’m looking for a YA or MG book about a teen boy who lives on a ranch (New Mexico? west Texas?), his cousin Horace comes to visit for summer which he thinks will ruin his summer but Horace turns out to be a good guy who can ride and shoot and they become good friends.  There is a mountain lion or cougar that kills his dad’s prize bull Red Toro so they go out to find the cougar, Horace shoots it with a great shot.  Along the way there are some villains who are trying to jump a gold claim, Horace sprains his ankle, has to be hauled out by the boy on an Indian trapezoid carry deal, they fool the bad guys into fording the river where there is quick sand and all ends well.  Can’t remember title.  Book had line drawings, and I think the cover was edged in burnt orange or brown.