Law of the Pampas(1939)

As rustled cattle have mysteriously disappeared, Johnny sends for his friend Hoppy, Hoppy arrives and immediately suspects Dan Slack. Realizing his telegram about Slack was intercepted, he locks up the operator Lafe knowing he can escape. Tailing Lafe he finds a secret entrance to a mine and inside finds the missing cattle. But Slack's men also find him just as the cattle are stampeded through the mine shaft.

Hoppy is busy chasing stagecoach bandits who sing as they rob.

Lee Garvin has eloped with the daughter of a railroad man who didn't approve of the marriage. Hoppy steps in when the young man is framed for murder.

European bad guy Baron Bendor leads some local townsmen in a plot to obtain horses through theft. Hoppy and his sidekicks Lucky and Speedy must find and expose the horse thieves.

Hopalong Cassidy and Johnny Nelson ride to the mountains to help a man and his daughter save their logging business from someone who is sabotaging their efforts.

When Ranger Hoppy's falsely accused young ranger friend is killed while supposedly trying to escape from jail, Hoppy is blamed and drummed out of the Texas Rangers.

A banker is trying to cheat people out of their silver-rich land. Hoppy learns that the banker is in league with an outlaw gang.

At the reading of his late cousin's will, California learns the estate will be divied among whoever remains of the seven relatives. With one already dead, another immediately murdered, and the Lawyer telling them the ranch is almost worthless, Hoppy investigates.

Belle Langtry runs a town being taken over by cattle rustlers. She is also a front for the outlaws, who are led by Steve Fraser. Hoppy gets elected sheriff and cleans up the town with help from the Bar 20 boys.

Hoppy and new sidekick California Carlson head to California to help out Lucky Jenkins.

Buck Peters arranges for Hoppy, California, Johnny and other cowboys to go to the aid of friends whose cattle are being rustled. Hoppy and California locate the rustlers' hideout and join the gang by posing as outlaws themselves, but must find a way to let the rest of the posse know where they are.

Hoppy, California and Lucky arrive at a remote inn, where Lucky expects to be married - but finds the bride-to-be in distress over her uncle, who has suddenly disappeared from the inn. Then Hoppy finds the uncle's body in the shaft of his nearby mine...