Most of the color comes from the group known as the blue-green algae, which display more colors than their name suggests. These thermal algae are extremely primitive and have probably changed little from those growing in hot springs at the very dawn of life on earth. Amid any Yellowstone thermal basin on a steamy day it is easy to imagine a volcanic region on a primitive earth where hot spring waters bubbled up through colored strands of these same types of algae and bacteria. _MAJOR FEATURES OF THE LOWER TERRACES_ _OPAL TERRACE_ Opal Spring flows at the base of Capitol Hill across the road from Liberty Cap. After years of dormancy, this spring became active in 1926 and began depositing up to a foot of travertine per year. In 1947 a tennis court was removed to allow natural expansion of the terrace. Further growth threatened the historic home next to Opal. Designed by Robert C. Reamer and built in 1908, the house is an example of Prairie Style architecture. Among Reamer’s other designs are the Old Faithful Inn and the Roosevelt Arch. Sandbags and an earthen wall today protect the house. It is the mission of the National Park Service to protect both historical and natural resources, which come in conflict at Opal Terrace. Should the spring be restrained or the historic house removed? _LIBERTY CAP_ This feature marks the north end of the Mammoth Hot Springs. It was named in 1871 by the Hayden Survey party because of its marked resemblance to the caps worn by colonial patriots during the Revolutionary War. It stands today as an extinct hot spring cone. Its outer surface has been cool and dry for many years and supports a plant community much different from that found at the active hot springs. Near the top are patches of orange lichen which are the pioneers at work breaking the rock into soil, paving the way for other plants to follow at some future time. PLEASE STAY ON THE TRAIL as weathering has loosened rock fragments which may fall at any time. _MINERVA SPRING_ Minerva Spring is centrally located within the lower terrace group and is easily accessible by trail from the various parking areas. This spring is a favorite not only because of its wide range of bright colors, but also for its ornate travertine formations. Since the 1890’s when the first records were kept on the activity of the Mammoth Hot Springs, Minerva has gone through a series of active and inactive periods. For several years in the early 1900’s it was completely dry, but by 1951 it was again reported that “Minerva is very active and certainly it is the most beautiful spring.” During the 1970’s spring activity has increased in some of the other features regenerating algae mats which now rival those found at Minerva. _JUPITER SPRING_