Fallen coniferous trees from 211-218 million years ago can be found scattered across the desert of eastern Arizona in the form of petrified wood. Made primarily from quartz, these geological wonders are actually fossils, and are often colored by additional minerals during the petrification process: Cobalt can create greens and blues, iron oxides create reds, browns, and yellows, and manganese can create pinks and oranges, just to name a few. From Wikipedia:
Petrified wood (from the Greek root petro meaning “rock” or “stone”; literally “wood turned into stone”) is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree or tree-like plants having completely transitioned to stone by the process of permineralization. All the organic materials have been replaced with minerals (mostly a silicate, such as quartz), while retaining the original structure of the stem tissue. Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material. The petrifaction process occurs underground, when wood becomes buried under sediment or volcanic ash and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition. Mineral-laden water flowing through the covering material deposits minerals in the plant’s cells; as the plant’s lignin and cellulose decay, a stone mold forms in its place.
There are petrified forests located all around the world — Argentina, Egypt, Namibia, India, New Zealand, Canada, and more — but Arizona’s Petrified Forest National Park has one of the largest concentrations of petrified wood on Earth.