Activities & Events
Pt. Lobos to Pt. Reyes: Evidence of ~ 180 km Offset of the San Gregorio & northern San Andreas Fault
N. California Geological Society
NCGS member Kathleen Burnham will lead a two-day field trip in the spring of 2006, as part of NCGS' contribution to the 1906 Earthquake Centennial
(A pre-field trip meeting will be held on April 26, 2006; please go the NCGS website for further details).
Participants will examine granitic rocks, conglomerate, and trace fossils at Point Lobos State Park, near Monterey, and then drive ~180 km along the San Gregorio and northern San Andreas faults to Olema, north of San Francisco. On day two, we will examine correlative rocks at Point Reyes National Seashore, as well as a 16 ft. (5m) offset of the 1906 San Francisco earthquake.
This will be an interactive, rather than lecture-style field trip. This trip will be substantially different from Clark and Brabb's 1996 field trip. The trip will probably include optional camping at Pfeiffer-Big Sur State Park on the preceding Friday night.
Roughly 50 million years ago, the granitic rocks and conglomeratic turbidites of Point Lobos and Point Reyes were parts of a single deep submarine canyon system. During the past 27 million years, they've been separated approximately 180 km by dextral slip of the San Gregorio and northern San Andreas faults. Similarity of these rocks has been noted as far back as 1899, but Kathleen's research establishes details which nail down the correlation. Her paleogeographic reconstruction has proved predictive: since its first introduction, other geologists have proposed four geologic and geophysical correlations which fit her model.
Point Reyes and Point Lobos are stunningly beautiful, and may be the only pair of localities on earth in which evidence of a large lateral offset is preserved in public parks at both ends.
Participants are requested to refrain from the use of aftershave, hand lotion, hair tonic, cologne, or other fragranced personal products, as the field trip leader is disabled by chemical sensitivity.
Saturday and Sunday May 20 - 21, 2006
Pt Lobos to Pt. Reyes
To visit evidence of ~180 km offset along the San Gregorio/northern San Andreas fault; To visit the Point Reyes Earthquake walk, to see the 1906 offset; To see evidence of the rearrangement and re-combination of faults through time; To consider whether between 23.5 Ma and 4 Ma two separate, parallel faults were active: the San Gregorio/northern (north of Bolinas) San Andreas Fault, and the Calaveras/central (south of Paicines, near Hollister) San Andreas Fault.
Professionals. Registration required.
Tridib Guha, (925) 370-0685