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President's Field Trip: Tertiary Sedimentary Geology of the Oregon Cascades

Wednesday, September 3, 2014 (starting time of day TBA) – Saturday, September 6, 2014

Join us for this year's President's Field Trip to Silver Falls State Park and the Eastern Cascades! Led by GSOC President Sheila Alfsen, this trip will feature Dr. William Orr as guest speaker on the western side of the Cascades and Jason McClaughry of DOGAMI on the eastern side.

Fee: $75, includes lodging for the nights of September 3 and 4 at Silver Falls State Park New Ranch House. Participants must supply their own bedding and mattress pad for this facility, or book their own motel room in nearby Silverton (not included in trip fee). 

Limit of participants 25, with a maximum of 8 vehicles for the trip stops (so we will be carpooling).

Deadline for registration is Aug 17. You may register for the field trip online, or send paper registration form to GSOC, PO Box 907, Portland, OR 97207, or bring to GSOC picnic on Aug 17th.

NOTE: You must be a GSOC member or guest of a member to attend GSOC field trips. Learn more about joining GSOC.

Step 1. Register online or
mail in registration form 


Step 2: Pay fee online or
mail check to GSOC, PO Box 907, Portland, OR 97207 

Pay Registration Fee Online

Step 3. Motel Reservations for night of Sept. 5th

Participants will want to secure their motel reservations for the night of September 5 in Madras. We have registered for group rates:

  • Inn At Cross Keys Station, 541-475-5800
    $95 single king/$99 double queen .
  • Econolodge Madras, 800-227-6865
    If participants mention that they are with GSOC, they will go by the group rate of $63 + tax for a one bed, and $72 + tax for 2 beds. 

Tentative schedule

Western Cascades

Day 1: Sept 3

The trip begins on Wednesday evening where we will be housed at Silver Falls State Park.

 After dinner, a talk by Dr. Bill Orr including:

  1. A brief summary of the area including structure and origin of Mt Angel.
  2. Tracing paleoshoreline regression using fossils.
  3. Outline of Scotts Mills formation, including:
  • Marquam member: tempestites, sea stacks, amalgamated sands, bioclastic limestones, offshore biostromes.
  • Abiqua member:  longitudinal dunes, bluff forming sandstone, both estuarine and marine.
  • Crooked finger estuarine, salt marsh deposits, freshwater marsh deposits with lignite lenses.

Day 2: Sept 4

Main focus will be middle Tertiary sediments and fossils in N. Marion County.

Formations: Little Butte, Scotts Mills (3 members), Molalla, Columbia River Basalt Group, and Willamette Aquifer.

Stops on trip: 

  •     Silver Falls
  •     Mt Angel
  •     Scotts Mills - Markham member, Abiqua Member, and Crooked Finger Member
  •     Columbia River Basalts and inverted topography
  •     Willamette Aquifer and diversions of the Willamette River Channel (Lake Labish)

     Evening Recap

East of the Cascades

Day 3: Sept 5

Travel to Madras - lodging at Chateau Inn or Crosskeys.

Look at features on Reservation- Mima mounds on Mill Creek Road, Structures on Tenino Creek Road.

Collect opals in road cut on US 97 south of Wasco/Jefferson county line.

Day 4: Sept 6

Main focus: Differentiation between Deschutes Formation and Simtustus Formation.

Possible stops (localities from Gary Smith’s paper in Oregon Geology Vol 48, Number 6, June 1986):

  • Overview of area from lookout (shown on the cover of publication) to see unconformity between two formations.
  • Upper Simtustus exposed on Clark Drive (upward fining fluvial cycles-1 km south of Gateway).
  • Roadcut on US 97 east of Gateway (cross bedded sandstone fining upwards to massive mudstone).
  • Gateway Grade (clastic dike), southwest of Gateway.
  • Lower Simtustus at Pelton Dam (upward fining fluvial cycles).
  • Volcanic debris flow deposits (type section north of Pelton Dam or Old Maids Canyon 5km southeast of Gateway).