Twilight on the Trail (1941)

"HOPALONG HAS HIS HANDS FULL...OF DOUBLE-BARRELED TROUBLE!... Range rats scatter when Cassidy crashes through with a BANG!"

Hoppy, California and Johnny come to the ranch of a friend and his daughter, disguised as dude detectives from the east, to investigate the disappearances, without a trace, of several herds of cattle.