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.
Saturday, September 26th
8:30 AM - 4:00 PM
Registration opens Thursday September 17th and is limited to 20 participants.
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 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. After a introduction, we will proceed west on Newport avenue, crossing a fault strand between 5th and 4th street, to 3rd avenue. We will turn right on 3rd and proceed to the north side of Bend and merge onto highway 20 towards Tumalo. We will stop at the Three Sisters Viewpoint (Stop 2) to group-up. From there, travel north to a wonderful exposure of a fault along Highway 126 (Stop 3). We will backtrack and head west of Highway 20 to start our traverse along the Tumalo Fault at Plainview (Stop 4). We will proceed to the south along the trace of the Tumalo Fault 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 then leave the Bull Flat area and re-connect with the Tumalo Fault as we approach Shevlin Park (Stop 9). We will then follow the trace of the Tumalo Fault to our the last stop in Northwest Crossing (Stop 10). After a neighborhood walk along the fault, we return to Pilot Butte.
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.
