This is Giant Western Comics 3, published by Mimosa (SA Magazine Co) in 1962.
It reprints all three stories from DC Comics' All-Star Western 101 (1958):
The Trigger Twins: "Sheriff on a spot"
Foley of the Fighting Fifth: "Ambush at Bear Paw Creek"
Johnny Thunder: "Johnny Thunder's Talking Shadow"
Also reprinted is this story from DC Comics' All-Star Western 98 (1957):
Strong Bow: "Three Defeats of Strong Bow"
Also reprinted is this story from DC Comics' Western Comics 48 (1954):
The Wyoming Kid: "The Last Stand at Fire Valley!"
Also reprinted is this story from DC Comics' Tomahawk 21 (1954):
Tomahawk: "The Frontier Inventor"
48pages, glossy colour cover, black and white newsprint interior.
The Mimosa cover image is taken from the Splash Page of the Johnny Thunder story from All-Star Western 108 (1959).
Here is the cover of issue 3 and DC Comics' original cover of All-Star Western 101 (1958):
Mimosa Western Comics Series