Clarence Edward Mulford (1883-1956) was an American author and the creator of the character Hopalong Cassidy. He was educated in New York. He wrote about 20 story featuring Hopalong Cassidy.
From the blurb:
Cassidy could fan a gun like a Bill the Kid... Six rounds in three seconds was his slowest time. No one in the state of Texas could beat him. Until he met Slim Travennes, head of the Sandy Creek Vigilante Committee. Slim was snake-fast. No man could go up against him and live. No man. Hoppy could stand or die. He had no other choice. None at all.
First publication date was 1907.
Source was Project Gutenberg.
Cover taken from original first edition.