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May 29, 2017
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The annual Avenue of Flags May 29 at RP Community Center SSU commencement; one for the history books Problem reaching AT&T last weekend? During Rohnert Park City Council meeting protestors unexpectedly take center stage Vehicle pursuit ends with arrest of 14-year-old Ex RP public safety officer pleads no contest to sex offenses Rancho 2017 top 20 Great turnout for RPPSOA pancake breakfast to help Project Grad Gabriella stole the show Town Hall meeting Sheriff's office releases details on SSU officer involved shooting A true celebration of ‘Cinco de Mayo’ Project Grad help in full swing Richard Crane Elementary School Suspect arrested after evading a Cotati Peace Officer Emiri Nomura awarded scholarship Shopping carts ran amok in Cotati last Saturday Ricardo Oliva receives ‘Coach of the year’ for the Northern District Sonoma State University equestrians jump with joy on their way to Kentucky Double Decker Lanes hosts the QubicaAMF Boys and Girl Club employee arrested for child endangerment Armed suspect arrested after resistance RP girl accosted while walking to school And they're off. . . Saddle Up and Ride Community quickly rallies for Project Grad Cotati opposes SB 618 Rohnert Park City Council to host Town Hall meeting on May 3 Graton Tribe makes good on payments Auto burglar arrested by Cotati Police A bit of Uganda A mission to help RP to replace old trees Engineering with Legos at the Ray Miller Community room Bunkers at Foxtail set for repairs RP man arrested for attempted murder CRPUSD OKs two contracts Credo gets used to new digs at SMV Golf Course Drive Crossing concerns may delay SMART train ‘Quiet Zones’ Man busted for DUI after crashing into tree in RP New hands bring subtle changes to Sharing of the Green fundraiser A traditional dance of Japan Shameful time in history RP rejects new self-storage facilities Survey Says: Rohnert Park Residents Love City, but not Traffic Council amends UDSP Body of missing woman found RAFD names part-time fire chief KRCB garners huge windfall from FCC auction Missing Penngrove woman's body found in Marin County Bunfest was hopping with bunny lovers Nonn expected to sue CRPUSD Credo crew marches to new home Cotati delays vote on Valparaiso The Voice enters into 25th year Cotati-reviews midyear budget Two RP Parks getting upgrades A new look for SSU gym RP man reported missing Padre Town Center changes hands Sonoma County to take a look at immigration issue Bomb scare closes RCHS Local Tech High student chosen for Scholars program RP to conduct survey Man arrested after high-speed chase through 3 cities RP makes changes to city code for ADUs Man gets 11 years in prison for RP knife attack Man who led chase into SF caught Treasurer for Rancho Cotate High Project Grad Arrested for Embezzlement A crab feast at Community Center Taking a pie in her grill RP man busted for possession of meth Cotati OKs water, sewer rate study RP votes to regulate vaping CRPUSD schools now a safe haven for immigrant students RP adds seven to public safety Cotati votes to host shopping cart race Man arrested for attempted murder Defibrillators proving to be invaluable assets Artists ready for art show at library Reilani Peleti Corrections Suspected explosive device at RCHS Seventh-graders in local schools to be taught CPR Voice issues apology to school board, superintendent RP man arrested on drug possession charges

The making of the Laguna de Santa Rosa

By:
May 5, 2011

Like all landscapes, the Laguna de Santa Rosa is the sum of many natural events. Long ago, deep-seated forces of sub-duction laid the foundation of coastal California. Tectonic forces shoved the eastern Pacific tectonic plate, formed at a volcanic ridge in the early Pacific Ocean, beneath continental rocks of the overriding North American plate. (Recall that sub-duction has caused the world’s largest recorded earthquakes, including the recent Sendai, Japan quake.)

Some 30 million years ago, the East Pacific plate’s mid-Pacific ridge began to disappear beneath North America. Starting from what is now northern Mexico and progressing northward, the San Andreas “transform fault” gradually replaced the sub-duction zone.

Now 810 miles long, the San Andreas Fault currently ends abruptly at Cape Mendocino. To the north, a small remnant of the East Pacific plate still dives into a sub-duction zone beneath North America, creating Mt. Lassen, Mt. Shasta, and the Cascades volcanoes of Oregon and Washington. Eventually, that plate and its ridge will disappear beneath North America, extending the San Andreas Fault to the Aleutian Islands.

Along the San Andreas Fault, rocks of the western Pacific plate were (still are) being shoved northward, grinding past the North American plate’s continental rocks at about two inches per year. The friction of the two plates encroaching on each other has warped and fractured the North American plate’s western edge. Early on, fragments broke off the North American plate and became welded to the Pacific plate margin, so southern Sierra Nevada rocks have moved northward over 300 miles to their current sites at Bodega Head and Point Reyes.

By about six million years ago, satellite faults had branched from the San Andreas and splintered the plate margin. The San Francisco Bay region was then a coastal plain. Sediments eroded from the North American plate were deposited across a shallow bay and adjacent landscape, on top of subduction zone rocks.

Between-plates pressures also have warped the North American plate’s margin into hills and valleys, similar to the rippling effect from pushing at the edge of a towel. The warping created a series of inland valleys and ridges between the San Andreas Fault and its generally parallel satellite, the Rodgers Creek Fault.

In Sonoma County these up-warps include the Coast Range, Sonoma Mountain, and additional ridges to the east. The Santa Rosa Plain is an oval basin between the Coast Range and Sonoma Mountain, with the Rodgers Creek Fault forming part of its eastern boundary. Creeks flushed sediments from flanking hills to progressively fill the Santa Rosa Plain basin as down-warping continued.

Located at the Santa Rosa Plain’s western edge, the Laguna de Santa Rosa marks its lowest elevations. Before European settlement, permanent to semi-permanent lakes and pools collected there during the winter and spring. For many tens of thousands of years, the basin probably contained much larger lakes from time to time.

Basin filling, and the various faulting processes continue today, making Sonoma County a very geologically-active area. The Sebastopol Fault forms the Laguna’s western (Coast Range’s eastern) edge. It may not generate earthquakes, but instead may reflect weaknesses in the rocks that at first folded due to warping pressures, then progressively fractured when no longer able to fold. In contrast, the San Andreas and Rodgers Creek faults do generate earthquakes, and we all need to respect their power.

Jane Nielson worked as a Research Geologist for the U.S. Geological Survey for 25 years. She is co-founder of the Sebastopol Water Information Group and Sonoma County Water Coalition.