Granite and Ice EarthCache

Yosemite is a glaciated landscape, and the scenery that resulted from the interaction of the glaciers and the underlying rocks was the basis for its preservation as a national park. Iconic landmarks such as Yosemite Valley, Hetch Hetchy, Yosemite Falls, Vernal and Nevada Falls, Bridalveil Fall, Half Dome, the Clark Range, and the Cathedral Range are known throughout the world by the photographs of countless photographers, both amateur and professional. Landforms that are the result of glaciation include U-shaped canyons, jagged peaks, rounded domes, waterfalls, and moraines. Glacially-polished granite is further evidence of glaciation, and is common in Yosemite National Park.

Glacier Point

Imagine one scene from Yosemite's past: Ice surrounds you. A chill wind blows above rivers of ice that originate at the Sierra Nevada crest and flow down the valleys. For most of the past few million years, ice dominated Yosemite's landscape. Repeated glaciations removed the soil, eroded the bedrock underneath and carried away tons of rock debris.

Now consider the spectacular view you experience today. The scene-shaping continues. Since glaciers have receded, rockfalls transform the shape of granite cliffs while rivers and waterfalls slowly wear away valley walls and floors. The results of these landscape changes are visible all around you in the magnificent view from Glacier Point.

The story of Yosemite's incredible geologic wonders is told, in part, by Eric Knight's series of dramatic panel illustrations, with permission to reproduce them here given by the National Park Service:

As tectonic forces uplifted the Sierra Nevada, powerful rivers and creeks cut Yosemite's canyons and valleys, carving the landscape into V-shaped canyons.

As the climate cooled, a series of glaciers entered river-carved valleys - plucking, polishing, and transporting rocks. The largest glaciers filled Yosemite Valley almost to the top of Half Dome.

Repeated glaciations eroded valleys, steepened granite walls, and sculpted many of the dramatic landforms we see today.

As the last major glacier melted and receded, Yosemite Valley filled with water and sediment, turning the Valley floor into a shallow lake. The lake eventually filled with sediment, creating a flat valley floor.

The extensive work of glaciers is visible throughout the park. Waterfalls leap from hanging valleys. Rockfalls from the glacially-steepened cliffs widen the Valley.

For over a century, Yosemite's geologic story has intrigued, inspired, and challenged visitors and scientists. The Yosemite Natural History Association built this Geology Hut as an observatory to educate visitors about Yosemite's geologic past. Take your time as you wander the hut and the surrounding areas of Glacier Point. Gather inspiration from this awe-inspiring landscape that is millions of years in the making and still being shaped and formed by incredible geologic forces today.

If you are interested here is a link for further reading about Yosemite's glaciers: Yosemite's Glaciers Today. Further reading about more of Yosemite's unique geology can be found at the following links: Yosemite's Geology, The Granite of Yosemite, and Rockfalls in Yosemite

Glacier Point is accessible by car from approximately late May through October or November. From the Glacier Point parking and tour unloading area, a short, paved, wheelchair-accessible trail takes you to an exhilarating (some might say unnerving) point thousands of feet above Curry Village, on the floor of Yosemite Valley. From mid-December through March, cross-country skiers can experience this view after skiing 10.5 miles from Badger Pass. A guided ski trip is available.

Logging Requirements:

1. Place the text "GC5B68N Granite and Ice" on the first line of your email.
2. Tell us the number of people in your group.
3. In what year did the Yosemite Natural History Association build the Geology Hut as an observatory to educate visitors about Yosemite's geologic past?
4. Looking at the illustrations panel in the Geology Hut, how many years ago did 'repeated glaciation erode valleys, steepen granite walls, and sculpt many of the dramatic landforms we see today'?
5. Waypoint 2: The spot you are standing on was under glacial ice during the period of peak glaciation. Take note of the elevation at this spot. Look out to the northeast at Half Dome. During glaciation of this area, the top of Half Dome was exposed, even during the period of peak glaciation. Take note of the elevation of Half Dome.
6. Waypoint 3: After you take the time to appreciate the vista laid out before you from this overlook, imagine the valley below you filled with a river of ice that extends over your head. What is your estimate of the distance to the valley floor from this spot?
7. Noting your observations of the elevations of Glacier Point, Half Dome and your estimate of the distance to the valley floor below you, what is your estimate of the thickness of the river of ice that flowed through Yosemite Valley during periods of peak glaciation?
8. Optional: Post a picture with you and your GPS at the location, making sure not to give away any answers in your photo!

Do not include any answers to the above questions in your log, even if encrypted, or we will have to delete your entry. If you do not e-mail us the answers to the above questions within a reasonable amount of time your log will be deleted.

• Would you like a two-fer? There is a USGS benchmark at Waypoint 3! Don't forget to discover it!
• Enjoy your visit to this world-class location! If you appreciated your stop here and the things you learned, please consider awarding this cache a favorite point!

Congrats to Team Bardini for snagging the FTF on this earthcache! Well done Sir and Lady Bardini!!