The third image in this series of vertical thrusts is a long vertical trail of brilliantly colored calcified rock that characterizes the stunning beauty of the Grand Prismatic Spring. The largest hot spring in the United States, it is known for its vivid colors, the result of pigmented bacteria in the microbial mats that grow around the edges of mineral-rich water. The color varies by season, and with the coming of spring, the orange and red colors replace the winter mats of dark green.