WYOMING, 1876. From the opening pages of the prologue it is obvious that the author of this long, leisurely western saga knows his territory and the wind-chapped people who inhabited that dangerous frontier. He explains in a postscript that he intended to place his fictional characters against a background as historically accurate as research and his own understanding could make it, and for this he deserves a whopping blue ribbon.

Ethnologists, military historians, and fussy critics may pounce on occasional mistakes. For instance, Cooke probably is wrong about the nonfictitious Frank Grouard: "When he was just a boy he had been found, naked and alone . . . " Dr. John Gray's investigation seems to prove that Grouard was a fully-clothed man, employed as a government mail courier, when captured by the Sioux. But on important points such as Lieutenant Grattan's idiotic behavior, the Sand Creek atrocity, Custer's attack on Black Kettle's village, and other examples of bluecoat bungling -- when writing about these matters Cooke displays impressive scholarship, and his narrative skill may be measured by the surprising fact that after a while we no longer distinguish between historical and fictional incidents.

Our story begins in three places. Ex-Army scout Chris Hardeman and his young sidekick Johnny Smoker are en route to a trading post called Putnam's Park. A black man named Julius Ingram and a Kansas runaway kid, Hutch, are forking hay in a snowy meadow near Putnam's. Lieutenant Ham Whitcomb is hurrying toward General Crook's army at Fort Fetterman.

Encamped near Putnam's is a band of Sioux governed by Sun Horse. They have been there, on and off, for years, living amicably beside the white intruders. Everything is just fine. Lisa Putnam and Chief Sun Horse are friends. But from the East come ever more whites -- emigrants and soldiers -- hungry for gold, hungry for battle. The Snowblind Moon is about this band of Sioux and the Putnam's Park settlers, who have lived well together and would like to go on doing so.

Now as we know, this could not happen because most 19th-century whites were alarmed by aboriginal life: " . . . they saw the feathers and the paint, the symbols on the tipis, the songs and dancing, the way of life so different from their own. They feared what was different, and so they would try to change it until they feared it no longer . . . They would take away the weapons and the horses, they would end the hunting; they would destroy all the symbols, seeking in this way to destroy the spirit."

These anxious whites looked forward to the subjugation and perhaps the extermination of Indians, and because theirs wasa majority attitude their ideas would prevail. Yet some whites seem to have understood Indians, liked them, and hoped to postpone or at least to moderate the forthcoming disaster. Cooke embodies these sympathetic people most notably in Chris Hardeman and Lisa Putnam.

It gets complicated, what with the entrance of Wild Bill Hickok, Crazy Horse, Hachaliah Tatum's peripatetic circus -- featuring an English giant, an elephant, a one-armed menace sporting a derby hat, a female clown who is Hachaliah's sex-slave, et al. -- Big Bat PouriEMere, Colonel J.J. Reynolds, Sitting Bull, He Dog, and dozens more. Nevertheless, Cooke's juggling act succeeds well enough that we can follow the action.,

Hardeman carries a message from General Crook to Sun Horse, notifying the chief that all Sioux must return to their assigned reservations by January or be declared hostile. Hardeman wants Lisa to persuade the chief that he must submit to Crook's demand, otherwise there will be a war which the Sioux cannot win. Lisa understands this, but she knows also that if the Sioux acquiesce they never again will be free. Thus, in microcosm, we observe the tragedy of the Plains Indian wars which reached a dramatic peak several months later at the Little Bighorn and concluded in 1890 with the slaughter at Wounded Knee.

Cooke writes graphically, sometimes indelibly. His description of Lieutenant. Whitcomb amputating Major Corwin's gangrenous leg is guaranteed to curdle anything in a delicate reader's stomach. "Dupr,e placed a stick of willow in Corwin's mouth for him to bite on but he bit through it and screamed . . . " Well, this is not a British novel of manners but a tale of early Wyoming.

Now and again Cooke relies on exhausted locations: "apt pupil," "lion's share," "unbridled fury," "hot pursuit," "broken English," and his phonetic reproduction of frontier lingo tends to parody. Excepting such lapses, he writes good, fluid prose.

Near the end of the novel Sun Horse deeds the Sioux valley to Hardeman, who discovers that this is the place where he belongs -- here with Lisa. It's just a bit sweet, as though illustrated by Maxfield Parrish. Even so, The Snowblind Moon is an intensely readable story crammed with authentic western lore, and John Byrne Cooke is a name to jot down.