Now we're on the weak end of the 'Lone Star' westerns. Unless you've never seen any of them, this is a retread of several tropes from earlier films in the series. If this is your first, the surprises at the end (which is well edited) will be new. Sorry to have to spoil your fun.
We get that dynamite is needed to clear the trail; dynamite is used to get water flowing in the superior first film 'Riders of Destiny' (1933). We get that John Wayne has really been sent by the government to work undercover and infiltrate the gang of outlaws; as also seen in 'Riders of Destiny,' and countless other early thirties westerns such as 'The Man From Hell's Edges' (1932) with Bob Steele, etc.
We get Lucille Brown as the "Prairie Flower," and Leroy Mason as the head villain, also from the better 'Texas Terror' (1935) in which Lucille gets more screen time than the villain, and when finding out that John Wayne is indeed a good guy at the end, rushes to his cabin to spend two hours alone with him! Unfortunately, she's wasted here with little to do. We get the Tin Lizzie driven by George Hayes, also featured in 'Texas Terror.' Note: In this film he sings a song! Now, if you don't think he's acting trying to walk and talk like an old geezer, watch him as the nasty, dastardly villain in the awful serial 'The Lost City'( 1935) ! We get shots of Yakima Canutt jumping on a horse, and plunging off a cliff into a river, among many shots repeated from earlier films in the series.
So what does it all mean? A weak Lone Star. When you have two extensive shootouts between the road workers and the villain's gang of henchmen behind rocks in a canyon, nobody, not even the camera, is moving. Surprise, that means that the film isn't moving either! It's better to spend your time on the 'Lone Stars' with either better character development or better action such as 'Sagebrush Trail' (1933),'The Star Packer' (1934), 'The Trail Beyond' (1934), 'The Dawn Rider' (1935) or 'Texas Terror' (1935). Despite the well paced ending, this one gets a 3.