Trip 2 PILLOWS IN WASHINGTON.
The basalt lava pillows at the south base of North Head are among the most spectacular I have ever seen, and in a beautiful setting. Pillow aficionados will love this place. Special thanks to my WWU grad school colleague Katie Kelleher who first told me about the pillows in this area. Here is the complete Geologic map of Cape Disappointment which includes the area shown in the figure below. Other pillow exposures in this series of articles are:
Get yourself to Cape Disappointment State Park on the Washington side of the mouth of the Columbia River near Ilwaco. Head for Cape Disappointment, and turn off WA 100 on the Jetty Road (State Park map) before you reach the Cape. Turn right toward Benson Beach and the campground at the south foot of North Head. Follow signs to campsites 161-170. Park at the restrooms at the loop road serving these campsites. If you traipse through campsite 166, you’ll find a trail that takes a direct route for 100’ to the first pillow exposures on the rock walls (46° 17.733’ N 124° 4.472’ W). If site 166 is occupied, there is access to the beach between campsites 167 and 168. Reach the sand, and walk 300′ north on the beach to the first small rock outcrop (46° 17.750’ N 124° 4.522’ W). Scramble inland over driftwood and through a narrow strip of trees to the plainly visible high rock walls, which are entirely pillowed basalt.
These pillows are part of the same story described in Part 1 of this series, Pillows in the Crescent Formation along the Heart of the Hill’s Road, Olympic National Park (link). However, below North Head they are even more spectacular due to wave erosion, which has removed softer and more soluble altered breccia and fine sediment that was once mingled with the pillows. The cliffs have sides facing different directions, so the stack of pillows is revealed at intersecting cross sections. There is no busy road, just the steady beat of the waves on the beach. Sea level has risen and fallen repeatedly; as recently as an 1885 map these rocks were seastacks just off the shore. Since then, sediment has accumulated on the north side of the North Jetty. If you continue along the sandy beach to the very foot of North Cape, you’ll find more wondrful pillow exposures. Close examination will depend on the surf and tide height.
Some websites claim that these rocks are part of the Columbia River Basalt Group (CRBG). This has not been demonstrated. A recent field trip guide (Wells and others, 2009), though it does not visit this site, provides a map similar to the one above. The authors are among the leading experts on the distal CRBG. They do not assign the North Head basalt to those far-traveled Miocene flows from eastern Washington.
Geology at Cape Disappointment is further described in Hiking Guide to Washington Geology by Bob Carson and Scott Babcock.
This place is NOT snow-covered in the winter. Winter is a good time to visit, especially if you like big surf.
Wells, R.E., 1989, Geologic map of the Cape Disappointment-Naselle River area, Pacific and Wahkiakum Counties, Washington: U.S. Geological Survey, Miscellaneous Investigations Series Map I-1832, scale 1:62500. On line: http://ngmdb.usgs.gov/ngm-bin/ILView.pl?sid=9948_1.sid&vtype=b&sfact=1.5
Wells, R.E., Niem, A.R., Evarts, R.C., and Hagstrum, J.T., 2009, The Columbia River Basalt Group– from the gorge to the sea: in O’Connor, J.E., Dorsey, R.J. and Madin, I.P., eds.,Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacific Northwest: Geological Society of America Field Guide 15, p. 737-774, doi: 10.1130/2009.fld015(32).