Pirates of the desert.

"The locals call the sand dunes of the Arizona Territory
southland a white ocean. One man, Barney Shivers, carries
the comparison a little further when he decides to
monopolize the shipping industry. Ordering his men to
attack any freight shipping that he does not control,
goods are stolen and held to ransom on the high seas. No
one dares to fight back until one little old lady Lolly
Amos, stands up to the bully. When the local law refuses
to help, Lolly contacts her nephew, Captain Parthenon
Downs of the Arizona Rangers. Restless to leave his desk
duty behind, Captain Downs eagerly takes on the challenge.
Little does he realize that his decision will draw him
into a war against two bands of pirates, and a young woman
with a Winchester rifle ... "--Publisher description.