This is probably old hat to most of you, but Ennis (or Innis, either is used) means "island" in Gaelic, and Del Mar is, of course, "in the sea" in Spanish. So Ennis Del Mar becomes Island in the sea, a perfect name for the psychological isolation of little Ennis after Earl's death. This might also be a reference to a poem by John Donne called "No Man is an Island," which contains the famous lines, "do not ask for whom the bell tolls, it tolls for thee."
In "The Mud Below," another short story in "Close Range," by Annie Proulx, one cowboy puts "A hand, fingers outstretched, ...across (the bull rider's) right shoulder, and against his chest. (The bull rider) did not know why this eased his chronic anxiety. But, in the way these things go, that was when he needed twist, to auger him through the ride."