You must find a mate in Amethyst Mountain and also have purchased the full version to be able to progress to the next episode. As soon as you have met this condition, a new zone will appear on the map accompanied by a star icon on the compass. Try going there!
In the trial/demo version, your game ends after finding a mate. You can still explore the slopes of Amethyst Mountain, harass predators and hunt prey, but you will not be able to progress to the second episode until you have purchased and installed the full version.
While you can optionally find a dispersal wolf and bond with them in Lost River, you cannot migrate to Slough Creek. This is intentional; realistically, the distance between Lost River and Slough Creek is never specified. There is no way of knowing whether your wolf and its mate would survive the journey. As for settling down and raising pups in this mysterious valley, it is neither safe nor an ideal location for a pair of wolves to settle and raise a family.