Back to All Events

President’s Field Trip: Lava Flows and Accreted Terranes

A Four-Day Carpool Trip to Visit Mesozoic and Tertiary Accreted Terranes and Miocene Lavas.

Rainbow Rock, Brookings

Rainbow Rock, Brookings

Our four-day excursion will travel down the coast to Brookings and across to Grants Pass before returning via I-5. The emphasis will be on the complex geology of the Mesozoic accreted terranes of the Klamaths but on the way we will take a look at Tertiary terranes of the north coast and interactions of Columbia River Basalt flows with coastal sediments.

We’ll be on the road from Tuesday, September 6th (the day after Labor Day) through Friday, with overnight stops near Coos Bay, Brookings, and Cave Junction.

Trip fee: $95 — Registration now closed.

  • Register by mail or online.

  • Apart from the trip organizers, entries will be accepted in the order received. If party size limit increases, additional entries will be moved in from the alternate list in the order received.

  • Refund policy TBD

  • Questions contact Bo Nonn

Trip Participation Policies

If you plan on participating in this trip, send in your registration form and fee. Each participant must be a GSOC member or guest and should have a separate registration form. A non-member may register only if he/she includes a membership application form and payment with the registration form and fee.

Minors must be accompanied by a responsible adult parent or legal guardian who is also a member of GSOC. Each participant must also fill out and sign a liability waiver at the meeting place in order to participate. Minor participants must also have the signature of a parent or legal guardian on the liability waiver. 

Apart from the trip organizers, entries will be accepted in the order received. If party size limit increases, additional entries will be moved in from the alternate list in the order received.


During the course of two reconnaissance trips we identified over forty noteworthy geological sites. We have time to stop at only a few of the best ones. The rest are described in the trip guide for those who might wish to explore on their own.

Day 1 Seaside to Coos Bay

We will meet on Tuesday morning at a park in Seaside for a brief look at the nearby tsunami deposit coring site. (We will not be doing the optional Saddle Mountain hike mentioned in an earlier announcement.)

The last stop for day 1 is near Florence but the first stop for day 2 is near Coos Bay, more than a hour's drive south. It is recommended that participants arrange lodging at Coos Bay and driving there after the last day 1 stop.

Day 2 Coos Bay to Brookings

We continue down the coast with stops emphasizing the Klamath accreted terranes and ophiolites. We will be joined for a lecture in the field by USGS and DOGAMI geologist Frank Hladky, who has written extensively about some of the stops. The overnight stop will be at Brookings, with abundant lodgings and a few campgrounds nearby.

Day 3 Brookings to Cave Junction

From Brookings we drive down into California and then up Highway 199 to Cave Junction. We will be accompanied by Roger Brandt, formerly with the USFS at Oregon Caves and a real expert on the Josephine Ophiolites. The third overnight stop is at Cave Junction; accommodations and campgrounds are nearby.

Day 4 Cave Junction to Portland

Ashland pluton-accreted terrane contact

Ashland pluton-accreted terrane contact

We meet at Oregon Caves. Prior to our tour our own Sheila Alfsen will fill us in on the cave and how it got there. Sheila’s from the area and worked for some time at the cave. For those who are not doing the tour Sheila will lead a modest hike in the area. From Cave Junction we will drive east to Grants Pass and south to Ashland to examine some remarkable contacts between a Jurassic terrane and a stitching pluton.

The formal field trip ends with an optional hike up Table Rock near Medford, a dramatic example of reversal of topography and unusual columnar jointed andesite. Those who do not choose to hike are free to head home. A number of supplementary stops and drive-pasts on or near I-5 are included in the trip guide for those who wish to see them.


  • Apart from the 4 mile Table Rock hike, most stops are relatively close to the road. Some stops may involve scrambling on rough beach access tracks and some beach walking.
  • Since much of the trip will be along two-lane roads with possible heavy traffic, we will not enforce strict car caravanning. Cars which get separated from the group can rejoin at the next listed stop.
  • Due to the small pullouts at some stops on day 3, we would like to limit the number of vehicles on this section of the trip. We will research options and notify participants.

The maximum party size has not yet been fixed. Initially we will try 25. If our third recon trip shows that we can accommodate a larger party, we’ll move people off the alternate list in order of signup.

Further questions contact Bo.


Registration by Mail or Online

1. Register by Mail

2. Register Online

Earlier Event: August 27
Board Meeting
Later Event: October 1
Mt. St. Helens Helicopter Tour