This is a great painting, I can see why you're fond of it, and western art from this period continues to fascinate and appeal almost like no other. Having said that, the artist, Victor Casenelli spent the majority of his long working life Muskegon, Michigan, far from the southwest. He moved from Cincinnati in 1905 after twelve years painting mostly seascapes and north African and Mediterranean subjects, but his love for American Indian culture and history became evident after his move to Michegan and remained the subject for most of his oeuvre thereafter.
His early works in Cincinnati are signed with the spelling "Casnelli" so yours spelled "Casenelli" is a later work, probably 1920s - 1930s in date judging by the frame which I am assuming is contemporaneous with the painting.
Victor Casenelli (1867-1961) did well for a self-taught artist and lived a long and prolific life. He was commissioned to do a number of murals including a series for former President William H. Taft and his work has long been accepted into the inventories of American Painting and Sculpture at the Smithsonian and many other museums and public art galleries besides.
As for value, his work has a steady and perhaps slightly growing following and his work is well listed.
Looking at comparables and going by similar subject matter, this composition entitled "Arizona Pass," a little smaller than yours at 10.5" x 19.5" sold at auction in 2010 for $2,500 and this example called "Along The Trail", a different medium (his preferred watercolor/gouache) and also smaller at 8 x 13 sold in 2012 for $2,200 are both representative.
Given its size and the fact that it's oil, yours would have an auction value in the range of $3000 - $5000.
If you saw it for sale in a high end art gallery it would have a retail price tag of at least $8000. This is also the replacement value for insurance purposes.
I do hope this helps!