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July 2010 - archives
Bull Run Watershed Tour 2010
by Janet Rasmussen
On Saturday, June 26, 2010, 22 GSOC members
embarked on a tour of Portland's premier drinking water source, the Bull Run
Watershed. We boarded a bus in NE Portland, and drove straight to our lunch
stop...
Oh, wait, while going through the town of
Sandy, we made a traditional stop at Joe's Donut Shop for donuts and pastries.
After our tour director took us through the
locked gates that protect this valuable water source, we drove up the twisting
narrow road to Bull Run Lake. This lake was naturally created about 10,000
years ago by a massive landslide that trapped its waters. Now the lake empties
underground, emerging some hundreds of feet downhill as a spring. The Bull Run
watershed was chosen as a water source for Portland back in the late 1800's,
first delivering water to storage reservoirs in Washington Park and Mt. Tabor
in 1895.
Bev Vogt, who did the mapping of this region as
her Master's Degree thesis work, explains her geological map, held by Joseph
and Marvel.
Bev and Bart Bartels have laid out samples of
each type of rock found in the watershed correlated to a diagram of rock layers
by age and position. The terrain mapped by Bev is steep, brushy, overgrown, and
virtually inaccessible, so these samples allow us to observe in a few minutes
what she spent months collecting.
After lunch and a very informative talk, we had
a few minutes to explore the three old cabins at the site of the lake. This one
has not yet been renovated. The massive old stove remains.
This cabin has been restored. Doug and I
admired the logwork. Logs for reconstruction came not from the Bull Run
Watershed, but from Canada.
Beargrass was blooming near the cabins.
We stopped later for a hike down a new trail to
the spring from which the Bull Run River emerges. Dwarf dogwood were blooming
along the trail. Fortunately, someone brought a flower book, or we wouldn't
have known what these flowers were. I did notice the four petals, which made
them resemble dogwoods, but didn't know there was a groundcover variety.
While driving toward the first of two dams, we
stopped to admire this waterfall across the canyon. Bev said there are many
more which are rarely seen.
The first dam holds back Lake Ben Morrow. It
was built between 1925 and 1929. The design is a curved concrete gravity dam,
similar in engineering to Hoover Dam, which was built later. The purpose was
for water storage and it also generates some power.
The caretaker's house at the dam has recently
been restored. It's being used for meetings.
The interior is charmingly redecorated, with
many original furnishings.
Doug stands by a massive table which is half a
section of tree.
An old oil lamp is hung in the living room.
Plaster casts of black bear footprints are on
display.
We walked across the dam, and also viewed the
Vantage Horizon which is exposed at the near end of the dam. The Vantage
Horizon is a layer of old soil (a paleosol) sandwiched between two flows of
Columbia River Basalt, which often contains fossilized wood. It's a very
distinctive layer that crops out in many areas of Oregon and Washington,
helping to establish the age and chronology of deposits. I was fascinated by
the long and narrow flights of stairs that were molded onto the front of the
dam on both sides, like an illustration in a Dr. Seuss book. Our tour guide
said that we could walk down these stairs and tour the inside of the dam. Those
who weren't quite up to walking down, took the bus and met us below.
The powerhouse of the dam, seen from above.
We begin the descent of the 240 steps down to
the base of the dam.
Wilven Smoody stretches out on the sheer wall
of the dam to peer into a mysterious square window.
GSOC members on the stairs. The inside of the
dam had two perpendicular tunnels. Photographs were not permitted. At the end
of the tunnel which ran parallel to the dam, dark stairs led up to a small
door. We were told these are steep, slippery and dark, and we weren't permitted
to explore further. We were thrilled to be allowed a glimpse inside this
massive old structure, upon which the city of Portland depends.
Our first field trip of 2010 was a great success!
Thanks to Clay Kelleher for arranging it, and Bev Vogt for her interpretations
of the geology.
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July 2010 - archives 