The hero, Texas Ranger Larry Whalen (Charles Starrett), is on the trail of a mysterious outlaw leader.

Sea Captain Windwagon Smith hits Westport, Kansas, the starting point of the old Oregon and Santa Fe Trails, and is quickly the laughing stock of the town; instead of traveling in the usual oxen-drawn covered wagon, he is at the helm and wheel of a Contestoga-type wagon with a full set of sails. He plans to go to Oregon by taking advantage of the prairie winds. First, he wins over the town mayor, falls in love with the mayor's beautiful daughter, Molly Crum, and then secures financial backing from the townspeople. He sets sail across the plains, with Molly Crum as a covered-wagon stowaway, and a Kansas twister looming on the horizon. And, then, the wind hits the sails. And the fan, too, if he had had one.

Roy is an oil prospector. His efforts to get drilling rights on an old Spanish land grant are countered by gamblers from an off-shore gambling boat determined to control the land (and oil) themselves.

Twenty years earlier Farrell killed his mining partner Andrews. Now Andrews daughter arrives to get her father's trust fund. Farrell having rustled Roy's cattle now takes her money from her Lawyer and lets her overhear false information of their next rustling job. With the posse at the wrong location, his men attack the cattle train and Roy on board find himself greatly outnumbered.

Thelma and Patsy get jobs at a radio station.

Steve Beaumont, an operative for the Cattleman's Protective Association, is assigned the difficult task of breaking up a murderous gang of rustlers led by Ed Brock and Strang. He takes Sheriff Webb, Judge Baxter, and rancher Ann Houston into his confidence, and works his way into the rustler stronghold and confidence by "turning rustler" himself.

The Kinkaids and the Harpers both run stage lines and are friendly competitors. Appleby is after the stage line and convinces the two owners to build a spur line to the same town. Then he has both projects sabotaged pitting the friends against each other and running them out of money.

After a handful of non-formula westerns, Charles Starrett returned to the mixture as before in Thundering Frontier. Starrett plays Jim Fillmore, kind to old ladies, small animals and heroine Norma Belknap (Iris Meredith). In contrast, the villains are kind to no one, least of all struggling building contractor Square Deal Scottie (Alex Callam), whose projects are continually targeted for demolition and his payroll is forever being stolen at gunpoint. A good 25 percent of the film's running time is given over to Bob Nolan and the Sons of the Pioneers, whose C&W croonings are pleasant but a bit much. One of the film's few surprises is that Starrett's perennial screen sparring partner Dick Curtis isn't one of the bad guys.

Lt. Col. Kirby Yorke is posted on the Texas frontier to defend settlers against depredations of marauding Apaches. Col. Yorke is under considerable stress by a serious shortage of troops of his command. Tension is added when Yorke's son (whom he hasn't seen in fifteen years), Trooper Jeff Yorke, is one of 18 recruits sent to the regiment.

The Pony Express is finished as the Post Office plans to award the mail contract to a stage line. Bill and his father put in a bid for the mail, however there are three bids close together. The officials will run a race to pick the winner, and the Banton Brothers sabotage Bill's stage. Mary still believes in Bill until they try to get rid of him by holding up the regular stage with his well-known horse. Bill needs proof to clear himself and expose the bad guys.