A very colorful hotspring near the Grand Prismatic Spring in Yellowstone Nationalpark. The colors result from dispersed silica (blue/green) which refract the sunlight. The warmer colors are small organisms (thermophiles) which live in hot springs and are colorful to absorb the sunlight. From those thermophiles the first enzymes for RNA/DNA analysis have been found. Also this was the cornerstone to our COVID vaccines today.
A petrified redwood-sized tree in the Yellowstone Nationalpark. Sadly, it is just one and the whole forests of petrified trees are quite difficult to access (very long hikes).
Marvelous hot spring with thermophile bacteria growing at the drain of the pool, yielding yellow, green and brown mats of bacteria. This is one of the numerous hot springs and geysirs near old faithful geysir.