Florissant Fossil Beds

A bloom of algae is the reason an insect that died 34 million years ago still has its wings.

This was a lake then, sitting at about 8,500 feet, much the same elevation as today. An active volcanic centre nearby, the Guffey volcano of the Thirtynine Mile field, kept throwing ash across it. Ash falling into the water fed blooms of diatoms, microscopic algae that build glassy shells. The diatoms died and sank in sheets, blanketing whatever had recently fallen in, and the alternating layers of clay, mud and ash compacted into what geologists call paper shales. Split one and you get an insect or a leaf recorded in a level of detail that ordinary lake mud would never manage. Berkeley's Museum of Paleontology rates Florissant, on the diversity of its flora and fauna, as one of the world's best known and richest paleontological resources.

Above ground the famous features are the petrified redwood stumps, left from a forest that stood among 150 plant species. One group, the Redwood Trio, is the only known fossil occurrence of a redwood family circle. Modern coast redwoods sprout new trunks from the base of a parent tree, particularly once the parent dies, and here that habit was caught in stone.

The site's history is a lesson in what unmanaged collecting costs. Tourists and excavators arrived in the late nineteenth century and the petrified forest lost much of its mass to people carrying the wood away. Real science ran alongside the souvenir hunting: the Hayden Survey mapped the area in the early 1870s, Leo Lesquereux described the plants, Samuel Scudder the insects, Edward Drinker Cope the vertebrates. Charles Whitman Cross formally named the beds in 1894. It took until 1969, and a long legal fight between local landowners and the federal government, for the national monument to be established.

Nothing leaves with you now. This is National Park Service ground, around 60,000 visitors a year, and the digging that still happens here is research.