stock footage from an earlier Durango effort, Galloping Thunder (1946), footage that included sidekick Smiley
Government Agent Steve leases land to Masters so he can bring in horses for the Army. Henley has obtained a forged lease for the same land and Steve is unable to prove it's a fake. While Steve checks with Washington, Henley plans to roundup and ship the horses. Masters also intends to roundup the horses and he has the Durango Kid on his side in the battle with Henley.
The Durango Kid, along with assistance from sidekick Smiley Burnett, investigates a pair of murders that threaten to fuel a range war.
The Durango Kid (Charles Starrett) returns to Ret Butte intending to sell his cattle ranch. Saloon owner, Duke Catlett (Lane Chandler) is the secret owner of a sheep flock which graze on the cattle lands--leaving them useless for cattle. A range war looms between the cattlemen and sheepherders.
World War II is raging and the manpower shortage has hit the range since every able-bodied cowboy of military age is off fighting for Uncle Sam. Dad Mathews, a rancher with a huge government contract order for beef, has trouble with the cattle rustlers, led by Henry Judson and Lefty Lewis, who are taking advantage of the situation to steal his herds. John Paul Revere, Special State Investigator, arrives, and upon meeting Mathews' daughter, Betty, gets the idea of recruiting the hard-riding daughters of the district into the WAPS, an organization which will be to the cattle country what the WACS and WAVES are to the Army and Navy. He trains them in military procedure and provides them with radio sending-and-receiving sets. Johnny's sidekick, Frog Millhouse, finds himself the possessor of a "walkie-talkie" which he considers just a "doo-dad" at first, but which is instrumental in the end, in helping Johnny and the WAPS trap the gang of rustlers in their hideout.
Western star Charles Starrett was amazing; he kept making the same film over and over, but always made it seem as if it was for the first time. In West of Sonora, Starrett once again plays a frontier good-guy named Steve (Steve Rollins, to be exact), who, when the need arises, disguises himself as The Durango Kid, masked righter of wrongs. This time, Steve/Durango champions the cause of 10-year-old Penelope Clinton (Anita Castle), who has spent her short life as the focus of a feud between her grandfathers, suspected outlaw Black Murphy (Steve Darrell) and Sheriff Jack Clinton (George Cheseboro).
The plot finds Steve/Durango attempting to capture ex-Civil War guerilla fighter Miller who may be the man who's been going around knocking down telegraph wires.
The election to determine if Texas will become a state is near and men opposed are running contraband across the border. Sunset and Frog are Border Patrolmen and have an agent that tips them off by carrier pigeon. The Army arrives and the commander is Sunset's brother. When the agent is found out and murdered, his fake replacement then leads the soldiers astray.