Using his sketches as study notes, Moran produced watercolor paintings that were highly finished versions of the scenery he had encountered. The sketch of The Great Spring on the Firehole River from Part I inspired this painting, in which Moran used a more extensive number of colors, applied to give a more solid sense of the forms. The Great Blue Spring (now called Grand Prismatic Spring) was especially suitable for the brush of a painter. The mist rising from the water often obscured the spring below. By studying the scene carefully, Moran was able to make an ideal picture of the spring, showing the water and its pure blue color, which were difficult to capture in photography. Notice Moran's distinctive monogram signature. He superimposed the initial "T" over "M" forming a "Y" shape. He became known as Thomas "Yellowstone" Moran.

Illustration: Thomas Moran, Great Blue Spring of the Lower Geyser Basin, Firehole River, Yellowstone, 1872, watercolor on paper. Buffalo Bill Historical Center, Cody, Wyoming. Purchased with funds from the William E. Weiss Fund, Mrs. J. Maxwell Moran, Wiley Buchanan, III, Nancy-Carroll Draper, Nancy and Nick Petry, Steve and Sue Ellen Klein, William C. Foxley, John F. Eulich, Mary Lou McDonald, IV, and D. Harold Byrd, Jr., 24.91.