The Little Ice Age was a period of glacier growth that extended from the late 1500's to about the 1850's. (c) This was a period of lower temperature on a global scale that brought about the advance of glaciers by an average of several kilometers at high latitudes and altitudes. Since glacier research in the Pacific Northwest did not begin until the late 1800's there is little direct information about the size of the glaciers in the Upper Skagit Basin during the Little Ice Age. Much of what we know is derived from mapping old glacial moraines and other post-glacial features. Because much of this work is in progress little is known about the extent of little ice age glaciers in the Skagit River Basin beyond the Silver Creek and Ross Lake Areas. (c) The glacier extents shown in this map are based on unpublished preliminary maps drawn by Austin Post, Wendell Tangborn, F. Rosenblatt, and Don Richardson of the U.S. Geological Survey.