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# Nick on the Rocks: The secret summit of Washington’s Mount Index
- URL: https://www.cascadepbs.org/environment/2024/12/nick-rocks-secret-summit-washingtons-mount-index/
- Published: 2024-12-27T08:58:46.000Z
- Updated: 2026-09-10T19:26:38.000Z
- Description: The mountain’s namesake granite was used to build Seattle’s iconic Smith Tower and is coveted by climbers. But its peak is made of a much older rock.
- Author: Adam Brown
- Tags: Environment, history, Multimedia, Video, Nick on the Rocks, Geology, Mount Index, mountain, #wp, #wp-post, #Import 2025-04-14 08:10, #Import 2025-05-09 12:31, #article

There is Index granite all over the Skykomish Valley. From the walls of the Index quarry – known by rock climbers all over the world for its grippy quality – to the towering peak of Mount Index, signs of the granite are everywhere you look in the valley.

However, the top third of Mount Index itself isn’t granite at all, but a much older and more mysterious igneous rock that formed more than 140 million years ago at the bottom of the ocean.

Nick Zentner travels all over the valley taking a closer look at the famous granite.

*Support for Nick on the Rocks is provided by Pacific Science Center.*