Original Signed Native American Ledger Drawing, Early to Mid 20th Century

I'm anything but an expert on ledger drawings, but I sure love looking at them, as much as anything else in the world. First generation Plains Indian drawings from the second half of the 19th century, representing first hand narrative accounts of battles and hunting scenes, are the best of the best, and way out of my reach. But this later one, I believe 1910s-20 though am not 100% certain, and which came from a private collection in Texas, really won me with its great flurry of flying arrows, wonderful pattens, animated expressions, and most of all the dramatic gesture of the central warrior captured mid-air as he leaps onto the horse of the cavalry soldier, dagger about to land. 

The manner of this graphite and colored pencil drawing makes me think it is Lakota, but again I am not an expert. Along the bottom edge is a signature, glued on, reading George Fincher (there are Lakota Finchers, which furthers my sense this is Lakota.) The paper is heavy stock ledger paper with page number 172 at upper right, and 171 on the reverse side. It measures 15 3/4" x 9 3/4" and is in very good condition, with no tears or creases. There is some ingrained dirt and minor staining/smearing. I photographed it standing on end which makes it appear a bit curled, but it lies flat.