Portland area Field trip
Stop 1: Hwy 99:
Waverly Heights Basalts (outcropping along Hwy 99 about 2 miles south of
OR City)
Oldest rock in OR area
Represents old oceanic
Eocene in age
Topped by CRBs
Great amygdaloidal textures
(secondary crystal growth of calcite in vesicles of basalt)
What is the red band in this
outcrop? This represents a bake layer
where the Col. River basalts flowed over the older rock.
Stop 2:
Formation
of the falls?
Large
into a weak spot in the river to
created falls. This process is known as
plucking
Stop 3: 205 overpass: CRB (Columbia River Basalts) (This is next to
Bottom layer,
Grande Ronde: 2 members
Winter Water & Sentinel Bluffs members ~15.5 mybp
Pillow lavas below bridge
Vantange horizon: This is a soil
layer that formed on top of the Grande Ronde
lavas. It has tree casts in it.
Second Layer,
Wanapum : 3 members: Ginko, Sand Hollow,
Sentinel Gap ~15.3 mpbp
Stop 4:
Top of Wanpum
basalt
Feature is a mini-version of
eastern
How much soil is present?
Where does the soil gather?
What is the elevation of this
spot? (~250 ft)
Stop 5: Quarry and Clackamas river road (you can’t go
into the quarry but the units are still visible. Also along Clackamas river road there are
many outcrops of the Troutdale formation.
This is a conglomerate that is poorly cemented together.)
Sandy river mudstone and
Troutdale formation (14-2 mybp)
What are these units made
from? Mostly clays, sands and gravels
Where did they come
from? They represent the time after the CRB’s when many rivers and streams dumped into the
Stop 6: Bathroom stop at Carver boat launch
Terraces…what formed
them? The terraces here represent old
river levels. The current river; step up to the
park; step up to the road; step up to the farmland above Clackamas river
road.
What units is the Clackamas river cut into?
Primarily they cut into the Troutdale and Sandy river mudstones.
What affect does this have on
stability of the area? Creates an area that is fairly
unstable with many landslides.
Stop 7:
Old quarry now made into a BB
court
What were they
quarrying?
General structure: Young Cinder cone (reactivated flow)
Cone erupted through troutdale
formation
Actual center near bathrooms
Part of Boring lavas (3mybp-80,000 yr)
This one ~100,000 yrs
Forearc
volcanism… fairly rare event
Cascade arc ~ 90 km above slab
Here ~50km above slab
Mountains uplift due to boring lava
magma at depth
Wall is made of rhyodacite ignimbrite from bend (brokentop)
Stop 8: Rocky
90,000 yr old boring vent
See many things from here:
Airport is deepest part of
Cascade volcanic axis is defined by mafic vents…(only in the South)
Mt St Helens and south.
Represents grabben
of southern cascasdes….allowed extension due to
rotation
Basalt will erupt
Grabben
is believed to be slowly extending into
Evidence of 40 floods in the valley
West side of rocky butte is gravel bar left by water
Several flood plains represented here
as col. River has cut through flood deposits
Modern flood plain : Horseshoe surface
Ingrim
surface 1000
yrs old
Winkle surface: 6000 yrs old
High Radon …flood gravels with micas
and feldspars
Stop 9: Max Station Zoo:
What group of rocks does the oldest rocks in this column represent and where did
they originate from?
As the rock types change,
what are some of the textural features you see and why do you think they exist?
In the basaltic samples, how generally,
does the distribution of the vesicles change from the top to the bottom of each
flow?
For the Grande Ronde lavas, there are two separate flows. Hypothesize as to what would cause the
discolored layer between them. Think
about the length of time the first flow existed before the second came along.
What does the Vantage horizon
represent?
Between the Grande Ronde basalt and the Vantage Horizon,
Why is the top of the basalt
so fractured and broken up?
Where the Wanapum
basalt contacts the Vantage Horizon,
there is a lot of inter layering of the two units. Why?
Why is the wanapum basalt so fractured where it comes in
contact with the