Upcoming Field Trips

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• Tumalo Fault Geo-Exploration

  • When
    25 Aug 2025
  •  
    8:00 AM - 5:00 PM
  • Location
    Pilot Butte State Park - lower parking area
  • Spaces left
    20

  Registration is closed

  
  

  

  Route and stops of the Tumalo Fault Geo-Exploration on the Geologic Map of the Bend 30- x 60-Minute Quadrangle, Central Oregon (I-2683) by D.R. Sherrod and others, 2004. Faults in the Sisters and Metolius Fault Zones are highlighted in red.

  
  

  Monday, August 25th

  8:00 AM - 5:00 PM

  
  

  Registration opens Monday August 18th and is limited to 20 participants. If there is greater interest, demonstrated by a long waitlist, we will schedule a second trip, likely in early September. Those on the waitlist will be given an early start on registration for a second trip.   

  
  

  The Sisters, on the east, and Metolius, on the west, Fault Zones combine to form a trend of 50+ northwest-striking normal faults stretching some 38 miles long and 4-10 miles wide. The 28 mile-long Tumalo Fault is the longest fault in these zones. Recent graduate studies by John Wellik (2008), MacKenzie Mark-Moser (2018) and Daniel Mongovin (2022); earlier work by Sherrod & others (2004); and information in the USGS Quaternary Fault and Fold Database, provide the foundation for today’s Geo-Exploration. Please join Bob TImmer, Hank Johnson and Derek Loeb for a traverse along the Tumalo Fault.
  

  The Geo-Exploration will start in the parking lot of the Pilot Butte State Park at the base of  Pilot Butte. We will then drive to the top of Pilot Butte for an overview of the regional geology and plans for the day. Then, we will proceed west on Newport avenue, crossing a fault strand between 5th and 4th street, to NW Bend  to start our traverse along the Tumalo Fault. From there, we will proceed to the northwest with stop #3 just past Shevlin Park, and then on to Bull Flat, the site of the failed Tumalo Dam. We will explore the geology and the history of irrigation at 4 stops in the Bull Flat area. We will continue to the north along the trace of the Tumalo Fault for about 4 miles to Plainview Road. Here we will end our traverse of the Tumalo Fault and head north to an excellent exposure of a fault in a roadcut along Highway 126.  We will then proceed east on Highway 126 to Cline Falls Highway and then south to the Tumalo Canal Historic Area. After a face-to-face encounter with an unnamed fault in the Sisters Fault Zone, we will end our GeoExploration and return to Bend.

  Today's traverse will be on the Geologic Map of the Bend 30- x 60-Minute Quadrangle, Central Oregon (I-2683) by D.R. Sherrod and others, 2004. While you can download this map, and very informative pamphlet, for free from the USGS website, your downloaded version will not be georeferenced. For those that want to follow today's  traverse using the Avenza app, you can download a georeferenced copy of the map HERE. 

  Total walking mileage for the day will be about 3 miles with modest elevation changes. Some walking will be on sidewalks, some on gravel roads and some will be cross country.  There is very little shade, but we will never be more than a half-mile  from the vehicles. Please bring a sack lunch, water and shade protection. There are no restroom facilities between the first and last stops. Total driving distance is about 65 miles of which 10 miles is on well graded gravel roads and the rest on paved roads. 

  The designated ride share meet up location is the parking lot on the east, and lower side of Pilot Butte State Park in Bend.

  Dogs are not permitted on COGS Geo-Explorations and Field Trips.

  Please note that this event is limited to 20 participants and registration must be done via the registration button on the trip listing on the COGS website.  Only COGS members and a guest may register.  Registration will be confirmed on the webpage by a light green box indicating registration was successful and by a confirmation email.  If you don't get this email you should try the registration process again.  Please contact Bob TImmer ( bobtimmer@yahoo.com ) with any questions.

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