From my parents' collection: "His Last Winter" by Robby McMurtry aka Aquasu, gouache/tempura on blue art board, dated 1974, 10.75x12.25, signed "Aquasu". Purchased at Oklahoma Indian Arts and Crafts Cooperative, Anadarko, OK in 1974.
A little damage to right upper quarter, please see photos, but it doesn't interfere with the image.
I love this painting, but we're running out of wall space! 
His art is getting rarer, since he passed in 2012. This is your chance to get a cool piece of art at a reasonable price.
Smoke-free/pet-free home.

Robby McMurtry (1950-2012) was an illustrator, novelist, painter, and playwright. He was also an art teacher who helped numerous young people through his work with Indian youth groups in eastern Oklahoma. McMurtry exhibited his work at many locations, including the Grand Palais in Paris, France. McMurtry’s work is included in the permanent collections of the United States Department of the Interior in Washington, D.C., and the Center for Great Plains Studies, University of Nebraska. McMurtry’s work was influenced by the stories he heard from his Comanche grandmother and his cowboy father, as well as the fantasy images of science fiction artist Frank Frazetta. After his death, McMurtry’s work was featured in a 2015 exhibition at the National Cowboy & Western Heritage Museum in Oklahoma City, Oklahoma.