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Oakley, California, United States

Big Break Regional Shoreline Exploration

The water flowing past Big Break Regional Shoreline via the Sacramento and San Joaquin Rivers drains 1/2 of California.

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Difficulty: Easy
Length: 3.6 miles / 5.8 km
Duration: 1-3 hours
Family Friendly
Overview: Big Break Regional Shoreline is a part of the great 1,680-square-mile San Francisco/San Joaquin Delta estuary in Northern California. The water flowing past Big Break Regional Shoreline through the Sacramento and San Joaquin Rivers drains half of California's watershed, and creates the largest estuarine environment on Pacific shores. This "Inland Coast" is home to 70 species of birds, and provides valuable habitat for beavers, muskrats, and river otters.

This Exploration created in collaboration with the Exploratorium.

Tips: Getting There
From Highway 4 in Oakley, go north on Big Break Road. Take the first right just past Vintage Parkway and follow the road to the Big Break Pier. You can also enter the park by walking in on Marsh Creek Regional Trail, just adjacent to Marsh Creek off E. Cypress Road in Oakley, east of its intersection with Main St./Highway 4.

Public Transportation
Tri Delta Transit #300 provides service to Vintage Parkway and Big Break Road on weekdays. Call to confirm route: Tri Delta Transit–(925) 754-4040 or see

Park Activities
Many park users come to Big Break simply to enjoy cool marine breezes in the summer. Birdwatchers are drawn by the constant birdsong from the marshes, and everyone comes to enjoy the solitude and escape from the nearby urban landscape.

The Big Break Regional Trail, which runs along the southern edge of Big Break through the Ironhouse Sanitary District, provides access for hikers, bicyclists, and equestrians to the southeastern edge of the estuary. The trail connects to the northern end of the Marsh Creek Regional Trail, providing access to Brentwood and Oakley. The Marsh Creek Regional Trail connects to the Delta de Anza Regional Trail via West Cypress Road.

Special thanks to Mike Moran, Shelly Lewis and Isa Polt-Jones of the East Bay Regional Park District for assisting us on this project. Robin Marks, Joshua Cassidy, Craig Rosa and Ron Wolf all contributed to this Exploration.

Points of Interest



Not long ago, this culvert was thick with blackberries. To bring it back to a wetland state, the channel was graded, letting water in from the delta. Shorebirds found the wetland the very next day. Now visitors see tule and cattails and even small fish. A lesson that sometimes simple, low budget restorations can do the trick; as long as they open up habitat, the critter will show up.

Beavers, Keep Out

Short fences around cottonwood trees keep them from falling victim to the park's beavers.

A good look at some beaver damage. If they were to chew the bark around the entire girth of the tree, the tree would die--if it hadn't already been knocked over and used to build a beaver den.

First Steps

The trail at Big Break welcomes bikes and wheelchairs as well as feet. Several miles down the road, it connects with other paved East Bay Regional Park trails, making it a nice starting point for a day's bicycle journey as well as a walk along the delta.

Green Delta

A pier over the delta provides a fine fishing and birding spot. On a clear day, you can see all the way to the Sierras. Watch the birds as they land and you'll notice that they avoid landing on the algae. To a shore bird, the algae appears from above to be a land, not water, and therefore diminishes the bird's potential habitat.

The algae floating in here in the delta is mostly non-native species, much of it Brazilian water weed that's made its way to the Delta from home aquariums. Once here, it finds an accommodating habitat and blooms, affecting oxygen levels in the water and driving fish populations away.

The Buzz About Mosquitoes

Naturalist Mike Moran explains that the bias against mosquitoes is purely human, as many other members of the Delta ecosystem relish them. (video)

A cloud of buzzing mosquitoes hovers over the water near the shore.

Sedges Have Edges...

With all these different plants waving in the marshy wind, how can you tell which is which? In this video, Naturalist Mike Moran rhymes his way to plant identification.

A bit of hands-on study showing what Naturalist Mike Moran means when he says "Sedges have edges, and rushes are round. Grasses are hollow from the tip to the ground."

A cross section view of a rush stem (left) and a sedge stem (right).

These waving green stems are often referred to as tule grass, but tule is actually a rush (meaning its round stems are not hollow like those of a grass). Ohlone and Miwok people used tules to make canoes which they used to get around San Francisco bay.

Tules are topped with distinctive brown flowers that produce seed heads.

This sedge plant has set up house along the water's edge, a common place to find sedges. This photo shows the edges of the plant's triangular stems. Sedges, like tules, flower at their tip tops and develop brown seed heads.

A closer view of the seed heads atop a sedge.

Cattails are a common sight in North American wetlands, and they are often the first plants to colonize a muddy area that has been cleared of other plants. The brown cylinder at the top is actually a conglomeration of many tiny flowers, which turn into seeds attached to a wisp. Cattail fluff was used during WWII as stuffing for life jackets, because it is quite buoyant. Native Americans used the fluff to line papooses and wove the leaves into walls and mats to waterproof them.

Cattail flowers become tiny seeds attached to a wisp of fluff that carries them through the air.

Rabbitsfoot grass (Polypogon monspeliensis) is recognizable by its bushy seed stalk. It is a hardy plant, and grows as an invasive species in many places throughout North America.

Unexpected Birding Hotspot

Big Break is a birder's paradise, with over 200 species throughout the year. On a good day along this trail, a skilled birder can probably find between 30 and 60 species in a couple of hours. (video)

The wastewater treatment plant provides a haven for birds at Big Break. The open water attracts shorebirds and the fencing keeps neighbors' pets away. Visitors can spot local birds here as well as many migratory species.

The wastewater ponds also offer birds--and hikers--a nice view of nearby Mt. Diablo, another stopping point for many migrating birds.

Caspian terns resemble large gulls, though their red bills make them distinct. Many of the terns in California are migrants from the Pacific Northwest, wintering over in warmer climes. Caspian terns are found on every continent except Antarctica, though their population in Africa and Europe has declined due to disturbances to their nesting sites.


Field of Yerba Mansa

Despite its scientific name (Anemopsis californica), yerba mansa is native to the American southwest, primarily in New Mexico. It now grows well in wet, marshy areas like the Delta. Though there is no documentation of it having a sedative effect, it is sold as a tincture similar to echinacea by some herbal remedy companies.

Don't be fooled: the large white petals aren't part of the yerba mansa flower, but rather its inflorescence, a flower-like structure that's really a collection of small flowers. The true buds are made of the tiny white petals that make a small tower of flowers in the center.

Also known as seaside heliotrope or quail plant, salt heliotrope likes briny soils, which makes it a good candidate for this area where two rivers meet the sea.

Tiny purple and yellow flowers bloom in rows on the salt heliotrope, and the plant sports thick, spade-shaped leaves.

The marsh monkey flower, also known as seep monkey flower (Mimulus guttatus) is one of many monkey flowers found in California. This species in distinguished by its love of wetlands. Without adequate water, the flowers dry up and disappear.

A close up of the marsh monkeyflower (Mimulus guttatus) reveals its characteristic red freckles along the outer sides of its yellow petals.

This invasive species is referred to as a pest by many wildlife biologists, and its prockly flowers only add to its lack of desirability. Starthisle often takes root after soil has been disturbed, and then grows quickly, blocking out chances for other species to regain a foothold.

When you see this weedy-looking plant with its forked leaves, steer clear to avoid scraping your legs on its spikes.

Otter Scat Dissection

Carnivorous otters making pit stops as they cross the road leave behind evidence of what they ate for dinner. (video)

White smudges along the darker gray asphalt mark a freeway where otters cross from one side of the road to the other. Mud and musk from their bellies gets dragged across the roadway, showing their path. They stop occasionally to leave little scat packages for the curious hiker to dissect.

The shells, scales, or feathers from recent otter dinners can be found in the scat left behind. The orange bits you can see here are crawdad shells.

A closer inspection might reveal some bones and even an occasional fish scale. Once in a while you might find feathers, evidence of a successful catch of a duck or grebe.


A varieagated meadowhawk (Sympetrum corruptum) finds respite on a spent yerba mansa blossom.


Walnut Tree Surprises

Fallen nuts gathered along the trail can become a simple art project. (video)

Hikers can keep an eye out for these small, dark nuts on the ground. They are from the California black walnut tree (Juglans californica), and while not grown commercially for human consumption, they are an important source of food for wildlife.

Before they fall from the trees, black walnuts grow encased in a thick green husk.

Crack a black walnut open and you'll find an inside that resembles an owl face. Try pressing them on an ink pad and making owl-face stamps.

The California black walnut is a common ornamental tree and grows well in areas like the Delta with a ready supply of moving water.

The bark of the California black walnut is notched and rugged.

The Big Break trail meets up with Marsh Creek and another 8 miles of associated trail. We end our hike here, but you can continue by foot or bicycle through more miles of East Bay Regional Park.
Pictures in this guide taken by: craigrosa
Wonderful trip

by Castellimark on Nov 21, 2010
excellent guide, one of the best I have seen

by foryoungfor on Nov 13, 2010

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Hi. I'm a Senior Interactive Producer for KQED in San Francisco, CA for KQED Science , which covers science,...

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