| Unalaska Formation | |
|---|---|
| Stratigraphic range: Miocene Era, Neogene Period | |
 Outcrops near Dutch Harbor, Unalaska | |
| Type | Geologic formation |
| Overlies | Aleutian Ridge |
| Thickness | 900–10,000 metres (3,000–32,800 ft) |
| Location | |
| Region | Aleutian Islands, Alaska |
| Country | United States |
| Type section | |
| Named for | Unalaska Island |
The Unalaska Formation is a Miocene Era geologic formation on Amaknak Island and Unalaska Island, in the Aleutian Islands archipelago of southwestern Alaska. [1]
It consists mainly of volcanic breccia, flows, tuff, and intercalated sedimentary rocks. [1] It is exposed over about 70 percent of Unalaska Island. The Dutch Harbor Member is a 126 metres (413 ft) thick Early Miocene sequence of the formation. [1]
It preserves fossils dating back to the Miocene era of the Neogene period. [2]
