In speaking of the great overland trail, which was used for a score of years after the discovery of gold in California, one is apt to think of it as of comparatively slight width. Yet, although it narrowed to a few miles in some places, there were others where the ground traversed was fifty or a hundred miles across. Thus it happened that trains which were following parallel routes were often out of sight of one another for days, and perhaps weeks. The breadth of the famous South Pass, the gateway of the Rocky Mountains, is so great that parties of emigrants frequently did not know for a long time that they were really traveling through it.