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Saturday, January 25, 2014


URBAN EXPLORER--Dinosaur Beach is located at the southwest corner of Pt. Loma, the expansive peninsula sheltering San Diego Harbor.
KNOWING YOUR TURBIDITES--With nothing much on the social calendar New Year’s Day, Pillar to Post staff went on a geological expedition to the west (ocean side) of Point Loma, the large peninsula north and west of the entrance to San Diego Harbor.  We were curious to see if the elusive Upper Cretaceous turbidites were in bloom.

After paying $5 (per car) we entred Cabrillo National Monument atop Pt. Loma.  We took the first right turn after the ticket kiosk and headed down the long, winding road to the west side of the peninsula.  If you’re headed to the tide pools at the tip of Pt. Loma go early as the line to get past the kiosk.

On the west side of Pt. Loma’s peninsula from the south tip to the Republic of Ocean Beach, the sandstone cliffs along the ocean are called the Sunset Cliffs.

Geologically these cliffs are technically known as the Point Loma Formation. They contain fossils, including dinosaur fossils, from the Late Cretaceous period, about 75 million years ago. The formation represents one of the few sites containing dinosaur fossils in the state of California.

The top of the peninsula to the turbidites formation shown in the picture above represents about 70 million years.  Turbidites are layered formations of sandstone that are made up of mixed rocks, shells and other materials that formed by the churning wave action.  This layering is totally visible along the beach just north of the lower Pt. Loma lighthouse.

The cliffs on the ocean side of the peninsula are sheer and are undergoing constant erosion due to wave action. On the east side the land slopes into San Diego Bay more gradually, so that homes and developments go right to the water’s edge. At the northern end of the peninsula the cliffs and hills become lower, disappearing entirely in Ocean Beach and the Midway area, where the trickling San Diego River flows.[

Let’s get back to those Upper Cretaceous turbidites.  Walgren’s has a shot that will cure your turbites.  That’s not true.  We digress.  The Upper Cretaceous is the last geological epoch in the Cretaceous. It began 100.5 million years ago, and ended 66 million years ago.

The Cretaceous is traditionally divided into Lower Cretaceous (early), and Upper Cretaceous (late), because of the different rocks. The rocks reflect the conditions in which they were formed.

The Cretaceous was the last period when dinosaurs were the dominant land animals. Triceratops, Tyrannosaurus and Velociraptor lived at this time. The huge Mosasaurus was the dominant marine predator. In the Cretaceous period, birds became more diverse. Flowering plants developed more, and became the dominant plants on land. The Upper Cretaceous ended 66 million years ago after a massive meteor hit the Earth causing an extinction event.

Species (66 million years ago) which depended on photosynthesis declined or became extinct because of the reduction in solar energy reaching the Earth's surface due to atmospheric particles blocking the sunlight. As is the case today, photosynthesizing organisms, such as phytoplankton and land plants, formed the primary part of the food chain in the late Cretaceous. Evidence suggests that herbivorous animals, which depended on plants and plankton as their food, died out as their food sources became scarce; consequently, top predators such as Tyrannosaurus rex also perished.

Bottom line:  Pt. Loma’s Sunset Cliffs area is one of the few dinosaur fossil areas in the State of California.  And, for $5 you can visit our dinosaur beach.

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