From the end of the Mesozoic to present, the region went through a series of uplifts and erosional sequences. Commencing 66 million years ago the Laramide orogeny was a period of mountain-building and erosion in western North America that created the ancestral Rocky Mountains. This cycle of uplift and erosion left behind one of the most complete non-marine Cenozoic rock sequences found in North America. Conglomerate rocks composed of quartzite and interspersed with mudstone and sandstones were deposited during erosion from a now vanished mountain range that existed to the northwest of the current Teton Range. These deposits also have trace quantities of gold and mercury. During the Eocene and Oligocene, volcanic eruptions from the ancestral Absaroka Range buried the region under various volcanic deposits. Sedimentary basins developed in the region due to drop faulting, creating an ancestral Jackson Hole and by the Pliocene (10 million years ago), an ancestral Jackson Lake known as Teewinot Lake. During the Quaternary, landslides, erosion and glacial activity deposited soils and rock debris throughout the Snake River valley of Jackson Hole and left behind terminal moraines which impound the current lakes. The most recent example of rapid alteration to the landscape occurred in 1925 just east of the park, when the Gros Ventre landslide was triggered by spring melt from a heavy snowpack as well as heavy rain.