Geology near the St. Croix River Valley

GEOLOGICAL  SOCIETY  OF  MINNESOTA

2008 Field Trip # 3 – Geology near the St. Croix River Valley

DATE:   September 13 (Saturday – 8:00 am to about 5:30+ pm)

LEADERS:   Dr. Anthony (Tony) Runkel and Terry Boerboom; both from the Minnesota Geological Survey

HIGHLIGHTS:    This trip will focus on the area of the St. Croix River Valley from near the town of Sandstone, MN to around Interstate Park at Taylors Falls.  The tentative schedule includes two stops near Sandstone and two or three near Interstate Park.  Note: Rock collecting in state parks is prohibited.  There may be limited opportunities for collecting outside of parks.

We should arrive by bus at about 9:45 am in the area of Sandstone, Minnesota to view the Hinckley Sandstone.  This sandstone is believed to be Proterozoic in age, and is a pure quartz sandstone that has traditionally been interpreted to be a record of the final stages of deposition in the Midcontinent Rift system, perhaps deposits of a delta that accumulated in a lake.  However, recent studies suggest that parts of the Hinckley Sandstone were instead deposited as wind-blown dune complexes.  The Hinckley Sandstone is also karstic: it contains small sinkholes that are developed over large open fracture systems, which permit rapid groundwater flow, much like the better known carbonate rocks of southeastern Minnesota.  Our stops will allow participants to view evidence for a windblown sand interpretation for the Hinckley, as well as some of the karstic features such as springs and large open fracture systems. [description by A.R. and T.B.]

Lunch in Robinsons Park in town of Sandstone.

In the afternoon we will travel to Interstate Park, where we will see Proterozoic basalt flows that are part of the Midcontinent Rift System. A half billion years after basalt flows were laid down at Interstate Park, they stood as steep-sided islands in the Paleozoic seas, and we will visit an outcrop that exposes the deposits of a bouldery shoreline along one of these islands in Cambrian time.  Additionally, there will be a brief discussion of the glacial-related history of the St Croix River Valley, including the formation of potholes developed in the basalt flows at Interstate Park. [A.R.]

WHEN AND HOW:    On Saturday morning, we will meet at Prince of Peace Lutheran Church and School, 7700 Monroe Street NE, MAP in Spring Lake Park.  Use the parking lot on the north side of the building (most distant from Osborne Road) and any parking spot away from the handicap parking area.  *see map on back*  We will take our lunches, beverages, and equipment (e.g. notebooks, cameras), leave our cars in the lot and climb aboard our Voigt deluxe coach (seats 56, with toilet, A/C, PA system, DVD, and Internet) and head for Sandstone, MN. Check-in begins 8:00 AM.  Please arrive before 8:00 to allow for a timely departure at 8:15.  We should return to the parking lot no later than 6:00 PM.

COST:    Cost of the one-day field trip includes the bus ride, guidance by two superstar geologists, and a written trip guide = $25/member.  Nonmembers pay $40.  Registration payment must be received by the deadline: Wednesday, September 3.  When 54 seats have been reserved, a waiting list will be started.  To register, send your check (payable to GSM) or money order (do not send cash) to:  GSM; c/o Diane Lentsch; 5533 43^rd Ave. So; Minneapolis, MN 55417 / Phone: (612) 725-0771.  Please include your name, phone number, and the names and numbers of any others that will be with you.  Also, include your cell phone number if you will have it with you on Saturday, so that we can reach you if you don’t show.  Participants must bring their own lunch and beverages.

PREPARATION:    Come prepared to have fun in any type weather or terrain.  Generally, sites will have mostly flat terrain, with paths, but perhaps a fallen tree or a few blocks of sandstone to climb across.  Each field trip participant will be required to sign a waiver of liability prior to the start of the field trip.  This is a one day trip.  You will need to bring a lunch and beverage.  No alcoholic beverages or smoking allowed.