Johnson Creek Watershed Geology Tour — Planning Page

Tour Overview

The tour will follow the geologic progression of Johnson Creek from its headwaters in the east to its confluence with the Willamette in the west.

Geologic sequence of Johnson Creek Watershed from Ma et al., DOGAMI Lidar-Based Surficial Map of the Greater Portland Area, Open File Report O-12-02, with Johnson Creek Watershed boundary overlay.

Headwaters

We will be looking at creek sediments in the eastern headwaters area to see if we can observe Troutdale formation (e.g. quartzites) or loess. Possible tour stops include #1 Cottrell Road, #2 Bluff Road, and #4 SE 282nd. The DOGAMI map O-12-02 (see Geologic Overview below) shows a division between "Windblown Sediments" to the north of Johnson Creek and "Ancient River Rock" to the south.

Buttes

Basalt cobbles eroded from the buttes are evident at #5 Regner Road. Hyaloclastic basalts and gravels are present at #11 Knapp Quarry if access is available. Otherwise the buttes are heavily vegetated (e.g. at #3 Wheeler Road and at #6 Nature Trail) making exposures of Boring Volcanics and Troutdale Formation difficult to find. Powell Butte has an excellent vantage point for viewing eastern watershed and buttes and may have loess exposures.

Missoula Deposits

Missoula coarse sediments outcrop at the creek at #8 Cedarville Lodge and #7 Main City Park. Leach Botanical Gardens may also have an interesting mixture of cobbles and boulders. 

Willamette Confluence — Waverly Heights Basalts

Waverly Heights basalt outcrops at Johnson Creek's confluence with the Willamette at #13 Klein Point (private property owned by Johnson Creek member) and #12 SE 17th. 

Other Issues

Collaboration with the Johnson Creek Watershed Council may allow us to explore related hydrological and environmental issues. 

 


Candidate Tours Stops from East to West

We will be looking at some of the candidate tour stops below to decide which are the most promising for our field trip later in 2017. 

Map of Candidate Tour Stops: Click on tour stop number for more info and link to Google Street View. Red lines are boundaries of the watershed and its sub-watersheds.

#1 Cottrell Road near headwaters

Creek sediments

Cobbles visible in bank in drainage (west across the road from impressive looking property and pond). Would we see evidence of Troutdale or loess? Access easy from road, but this may be private land.


#2 Bluff Road

Creek sediments

Bank west of road has cobbles and silt layer. Presumably this is Troutdale and perhaps also evidence of loess. Access a little tight from road.


#3 Wheeler Road

Heavily vegetated butte terrain

Stream in steep canyon on first Boring butte in watershed. Heavily vegetated, so no outcrop visible.


#4 SE 282nd

Creek sediments

Cobbles visible from road. Not sure what access will be like when water level is lower.


#5 Regner Road

Basalt creek cobbles

Access down steep bank from bridge. Boring cobbles/vesicular basalt visible at this point. 


#6 Nature Trail

Heavily vegetated butte terrain

Nature Trail to top of Boring butte. Good field trip stop, but heavily vegetated so I couldn't find an outcrop.


#7 Main City Park

Missoula cobbles

Map shows Missoula coarse sediments. Good field trip stop, but access to bank restricted because of erosion concerns.


#8 Cedarville Lodge

Missoula cobbles and sorted sediment

Presumably Missoula cobbles on far (southern) bank. Interesting sediment sorting in creek. Good access from public park


#9 Powell Butte

Viewpoint and loess

Great views of buttes and eastern watershed. Good interpretive materials, including material on Native American "ceded lands." Map shows "windblown sediments" at top, however this area is heavily landscaped. Significant trail system, so perhaps worth exploring to see if there are either outcrops of Boring or Troutdale.


#10 Leach Botanical Gardens

Creek cobbles and boulders

Good access to cobbles/boulders under 122nd Ave. bridge. Not sure what geological resources Leach Botanical Garden might have.


#11 Knapp Quarry

Boring volcanic basalt and gravels

Stop is described in GSA Field Guide 15 (2009) as follows:
"Massive basalt crops out at the top of the slope above the road. Exposures in the walls of the small creek reveal beds of palagonitic hyaloclastite and underlying gravels. Mount Scott (Fig. 3) is a shield volcano, one of the larger centers in the Boring field.

The flows exhibit LKT compositions similar to the Cascadian LKT flows (Table 1, #8) but were erupted locally. The palagonitic sandstones and gravels indicate basalt-water interac-tion in a fluvial setting. Generation of hyaloclastite was likely a common occurrence during eruptions within the ancestral Portland Basin, but deposits of these events are rarely preserved except where, as here, they were buried and protected by lava flows. All Mount Scott lavas sampled exhibit reversed polarities (Fig. 6). Ages obtained for Mount Scott lavas are 1.6–1.5 Ma (Table 2). These eruptions ended a roughly 750,000 yr quiescent period and began a period of relatively continuous activity that continued into the late Pleistocene (thus far). This was the last time that LKTs erupted in the Boring Volcanic Field."


#12  SE 17th outcrop

Waverly Heights basalt

Presumably Waverly Heights basalts of SE 17th. Haven't visited this site yet, so not sure of access.


#13 Willamette Confluence (Klein Point)

Waverly Heights basalt

Waverly Heights basalts at Klein Property at Willamette Confluence. The Kleins are Watershed Council members and would give us permission to access the north side of the confluence for the field trip. Public access on south side is quite steep