What in the first two paragraphs on pages 331-332 support the idea of realism?

Example of Realism, paragraph two.....

The one thing that relieved the whiteness was a thin dark line that curved from the pine-covered island to the south. It curved into the north, where it disappeared be hind another pine-covered island. This dark line was the trail—the main trail. It led south 500 miles to the Chilcoot Pass, and salt water. It led north 75 miles to Dawson, and still farther on to the north a thousand miles to Nulato, and finally to St. Michael, on Bering Sea, a thousand miles and half a thousand more.