Tuesday, August 28, 2012

Haystack, North Cascades

I was taking a look at some of the North Cascade glaciers including a couple in my graduate field area - the McAllister Glacier and the Borealis Glacier. My field work in graduate school did not include glaciers other than I spent a fair bit of time walking on them as a means to get to rocks as my field area contained a large concentration of glaciers. While looking at the glaciers on Google Earth and the USGS programs, I thought to mark up some highlights of my graduate field work area including geology as well as other non geologic observations. A bit of memory land perhaps. More on the glaciers on a future post. For this post Site #1: The Haystack.
My graduate field area in the North Cascades - The Haystack indicated by #1
View of the Haystack somewhat obscured by Will
The Haystack has a haystack profile. The Haystack consists of a single pluton of diorite. This pluton was a significant part of my thesis effort. Th Haystack Pluton solidified at great depth and was surrounded by high pressure metamorphic rocks. Just to the east is another pluton - the Eldorado Pluton that had been dated at 90 million yeras old but had solidified at a much shallower level in the crust. The rocks around the Eldorado all contain high pressure metamorphic minerals. This feature had been previously recognized and the pressure disparity between the Eldorado and the high pressure surrounding rocks as well a lots of sheared rocks near the Eldorado Pluton margin suggested a fault line. That fault line ended up on most maps of the North Cascades and was large enough that it was shown even on the State geology map. My initial thesis goal was to figure out that fault. When did it move? What was its geometry? How much offset?
At the time the age of the Haystack Pluton was not yet known. Getting its age required collecting about 60 pounds of it and hauling it out of the mountains. The 60 pounds of rock were then run through a rock crusher and ground down to a fine sand. The sand was then run through a shaker table with water much like panning for gold to separate out zircons, a mineral rich in uranium and lead. The zircons were then sent to Nicholas Walker at the University of Texas who figured out the lead and uranium isotope mix and the age of the pluton.
The age determination for the Haystack Pluton was 75 million years. Hence, this rock hauling excersize allowed for placing an age constraint on the when the rocks between the the Eldorado Pluton and Haystack Pluton were deeply buried.
Topographic map of the Haystack area (USGS)
Aireal view of above topo map (USGS)
But there were some other non geologic highlights at this site. First and foremost was it was a very tough hike to reach the camp site on the west side of the above map. It required about a 5,000 elevation gain on the trail up to a ridge above Monogram Lake then a drop down to the lake and then another 1,000 feet cross country without a trail to the camp location.
Hauling gear and 60 pounds of rock for dating down hill was not a very pleasant task as it beat the heck out of my knees. I had originally requested a permit to fly my camp in via helicopter, but with the proximity of Monogram Lake as a destination with a trail, the National Park turned me down. On my second trip into the area after hauling the dating sample out, a helicopter flew directly over us. Curses were shouted! 
Because we had to leave camp all day long to work, I was very concerned about bears. A previous researcher in the area had his camp destroyed by bears while out mapping during the day. Hence, I set camp right next to the glacier in an area surrounded by about a square mile of bare rock. The air flowing off the glacier made for chilly evenings, but camp was left in tact. And we did see plenty of bears. We joined them is eating pounds of blueberries. One bear led to a long debate between Steve and I as to whether or not the bear was a grizzly bear or black bear. I have since come around to Steve's view that it was a grizzly bear based on its shape.  

No comments: