The high Uintas were extensively glaciated during the last ice age, and most of the large stream valleys on both the north and south sides of the range held long valley glaciers.[8] However, despite reaching to over 13,500 feet (4,110 m) in elevation, the climate today is sufficiently dry that no glaciers survived even before the rapid current glacial retreat began in the middle nineteenth century. The Uintas are the most poleward mountain range in the world to reach over 13,000 feet (4,000 m) without modern glaciers, and are in fact the highest mountain range in the contiguous United States with no modern glaciers. Permafrost occurs at elevations above 10,000 feet (3,000 m)[9] and at times forms large rock glaciers.