Gaylord Riley fell in with outlaw Jim Colburn when he helped Colburn out of a scrape in a saloon, but he never really became the outlaw type during his two years with the gang. Colburn and his gang may not have had their hearts totally in the game either, because they recognize Riley's unsuitability for the lifestyle and talk him into taking money and starting a ranch. Riley had spent his life wandering the west, searching for the men who had wounded him and killed his father, but at the gang's urging he takes their stake and begins to build with it in the Dark Canyon Wilderness of southern Utah.
He's a later entry to the area, centered on the small town of Rimrock and the ranch of Dan Shattuck. Saloon keeper and brothel owner Martin Hardcastle is the main man of Rimrock and has eyes for Dan's niece Marie, but Dan makes it clear a brothel owner is not fit for his niece's company and stirs a deep hatred in Hardcastle. Riley's arrival offers him a chance to create a scheme for revenge and Riley's slightly shady reputation provides an excellent way to be rid of him once his task is done. But Gaylord Riley is nobody's fool, and Marie Shattuck is no shrinking flower...and she loves Riley, not Hardcastle.
On the one hand it's easy to say that Canyon needs to be a little bit longer, so we can see some of Hardastle's machinations at work. His plans are a little too opaque for top narrative smoothness and his endgame moves seem to make all of the earlier plans unnecessary. The gaps also leave L'Amour in a position of having to tell us some of the things that are happening rather than show them, and that choice rarely does a story much good.
But on the other hand, being kept partly in the dark puts us in the same boat as Riley -- we know like he does that something is going on and that it's not good, but we can't quite sense what it is. The knowledge gap means Riley's toughness, speed and honor can't be brought to bear on his enemies...because he doesn't know who they are or what they're planning.
Dark Canyon is full of the touches that show why Louis L'Amour reigned as the king of the Western novel for so long (and why, in the minds of certain middle-aged grump types he still does). The opening sentence sets a hook that keeps an iffy reader going long enough that even when he or she runs into some of the less clear or less well-drawn passages the result is a shrug and commitment to finish out and see how the book ends. With a quick paragraph he lets us know that Dan Shattuck and Martin Hardcastle will have business with each other before we're done. Characters that a lot of writers would use as nameless cannon-fodder get real story arcs before leaving the stage. with an economy of words that seems to come so easily to the old pulp-era writers. And of course there's the descriptions of the magnificent wilderness where L'Amour chooses to work.
This may not have been one of L'Amour's front-rank works like Hondo or The Daybreakers, but the reader who doesn't particularly care for it will only be troubled for 120 pages or so before finishing it and reaching for one of the hundred-plus other novels he produced and finding one that better suits.