Buck rules Judge Miller's place in the Santa Clara Valley, a hundred and forty pounds of him, out hunting with the Judge's boys, until a gardener's helper steals him and sells him north into the Klondike rush of 1897. A man in a red sweater teaches him the club; the traces teach him the rest. He fights Spitz, the lead dog, for the front of the harness, and watches a dying dog bite through another's traces rather than be cut out of the work. Then John Thornton takes him on, and the last third turns into a love story between a man and a dog. Thirty-one thousand words, and much more brutal than its usual shelving with children's books suggests.
The Call of the Wild is 31,756 words. At an average adult reading pace of 300 words a minute that is about 1 hr 46 min, or roughly 1 hr 19 min if you read quickly and 2 hr 39 min at a more deliberate 200 words a minute.
That count is measured from the complete public-domain text rather than estimated from a page count, so you can compare all the books side by side.