Prairie Pioneers

Soon after the Mexican-American War and California's admission to the United States, "Stony" Brooke, "Tucson" Smith and "Lullaby" Joslin, friends known as The Three Mesquiteers, lead a group of settlers to Provedencia Valley in California. Meanwhile, Don Miguel Ortega and his children, Roberto and Dolores, discuss with their friend, Carlos Montoya, the problems arising from the "Americanos" invading Spanish-owned ranches. Telling Don Miguel that he will be forced out by the settlers, Montoya tries to persuade him to sell his large ranch, but Don Miguel refuses. Unknown to the Ortegas, Montoya is working with hydraulic gold mine owner Fields, who wants to strip-mine their land. Upon hearing that some Americans have entered the valley, Roberto and his vaqueros investigate and become embroiled in an argument with the four settlers, who refuse to believe that they are encroaching on the Ortega ranch. As the argument turns violent, it is broken up by the Mesquiteers, who are riding by. Stony blames the vaqueros, but Tucson, who has been friends with Roberto since childhood, believes his side of the story. While Don Miquel is inviting everyone to put aside their differences and come to a fiesta at the hacienda the next evening, Carlos plots with disgruntled setters Morrison and Wade to fuel the fire between the Spaniards and the setters and thereby obtain the Ortegas' land. Just before the fiesta, Roberto receives a note, allegedly from Tucson, asking him to come to the settlers' camp. When Roberto goes to the camp, he is ambushed by Morrison and Wade. The gang then puts on Spanish outfits and attacks two sentries while destroying the settlers' camp. Wade goes to the hacienda and tells the others of the attack, and when they rush to the site, they find Roberto in a daze. Wade shoots Nelson, one of Roberto's pursuers, and the crime is blamed on Roberto, but Tucson, believing his claims about the note and ambush, helps him escape from the mob. Soon after, Wade stirs up the settlers into attacking Don Miguel, but Stony saves the old man, who suffers a nervous collapse. Stony convinces Dolores to tell him Roberto's hiding place so that he can be brought back to comfort their father, but when Montoya learns what Dolores has done, he sends word to Army Captain Blake to follow Stony. Roberto is arrested and he, Tucson and Dolores mistakenly blame Stony for his capture. After Roberto is tried and convicted, Stony and Tucson become suspicious of Montoya and soon uncover his schemes with Fields. The two friends patch up their differences, and with Lullaby's help, set out to find the necessary evidence to prove Roberto's innocence before he is shot by a firing squad and Don Miguel sells his land to Montoya. The Mesquiteers find the disguises used by Wade and the others at the mine headquarters, and after a shootout with the gang, Stony and Tucson take Wade to town just as Roberto is about to be executed. Wade confesses that he killed Nelson and implicates Montoya and Fields in the affair. Lullaby and Tucson round up the two men, after which the Mesquiteers receive the Ortegas' thanks.