Wednesday, September 30, 2009

Antelope Island geology field trip

Sunday I joined 27 others on a hike around Antelope Island State Park courtesy of the Salt Lake Chapter of the Association for Women Geoscientists. Some of you Lucy family members will remember this park as the place we went before our wedding to "experience" the Great Salt Lake. Sunday was a day to look at evidence of past climate change and hike with other women (and a few men) geologists.

View northwest from Buffalo Point. You can just make out a line of a few hikers on the trail down below.

As we hiked on the Bridger Bay trail we were more or less on the Gilbert Shoreline of Lake Bonneville (marked by an arrow in the picture above), which formed about 12,000 years ago by Lake Bonneville as it paused at this level for some reason when the global glacial period was changing to a warmer, dryer interglacial period. The highest stand of Lake Bonneville would have been almost 1000 feet over my head as I stood here. That shoreline and others are clearly visible as we looked across White Rock Bay. Can you see the shorelines on this picture? (You can see a larger picture if you click on it. Really. Just do it.)

Could pick out the shorelines? OK, it was a pretty hazy day, plus you probably didn't click on the picture did you? Oh well, I'll give you the answers anyway. On the picture below are marked the Stansbury (green) level from 24,000 years ago, where lake level stabilized for a thousand years as the lake was filling. By 18,000 years ago the lake had risen to the Bonneville level (blue), its highest level, during which time it was fresh and HUGE. Lake Bonneville was 325 miles long and 135 miles wide and reached into Nevada and Idaho. This is the level of the lake I was talking about when I snapped this picture a few weeks ago out in the West Desert. A natural unconsolidated sediment dam up in Idaho broke and drained the lake to the Provo level (pink) by about 16,000 years ago. As the climate dried, so did the lake, evaporating to the Gilbert level (orange), after which it kept drying to where it is today.
And we humans have a conniption when the Great Salt Lake rises 10 feet as it did in the 1980s!

We saw antelope on Antelope Island. That was a surprise. In the dozen or so times I've been to the island, I have never seen antelope there. I have always seen buffalo though. There is a managed herd of American bison (Bison bison, now there is one Latin name I can remember) roaming freely. I managed to accidentally create this cool shot.

Another of my marginally artsy photos. Maybe I should stick to geology.
Anyway, hope you enjoyed this little climate lesson. Our next post will be about biking again.


  1. Awesome post. So first of all, I did click on the photo. Second, I'm taking a print-out of the color-keyed shoreline photo next time I head up there. Thanks for doing that- very helpful.

    More geo-posts!

  2. Thanks, Watcher. Antelope Island is a great place to look at Lake Bonneville Shorelines. Stay tuned for more geology disguised as biking trips.