Shollenberger Trail Guide

By Gerald Moore
Updated by John Shribbs, 2021
trail map

Shollenberger Park Self Guided Tour

Station 1 – Birds and Their Adaptations

How many different species of birds can you see from where you are standing? What is the shape of their body, legs, and beak? Are they floating on the water, perched on a plant, or standing on the shore? Because each species of bird is adapted for a different feeding style, competition for food is reduced. Shorebirds find food at different depths in the mud in proportion to their bill length. Egrets and herons can feed in deeper water, stabbing fish with their sharp beaks. If you see the Snowy Egret, watch how it wiggles its yellow feet in the water to attract fish. Mallards tip up and dabble in shallow water. Ruddy Ducks dive in deeper water and feed on the bottom. Many of the species of birds you see here are year-round residents, building their nests and raising their young. As you continue to walk, keep your eyes open for the Common Yellowthroat and look and listen for Song Sparrows with their lively and varied song of short notes followed by a trill.

Station 2 – Geology

Around 10 million years ago, the ocean that covered this area was receding. Several tectonic plates were moving against each other. The movement of the earth and the pressure associated with it, pushed the mountains up and pulled the valleys down. Volcanoes developed and erupted as a way for the earth to release its stress. Three to five million years ago, Sonoma Mountain, the long mountain to the east, was a volcano and the valley in which you stand was approximately 1000 feet deeper than it is now. Where did the volcano go? Much of the volcanic debris eroded off the mountains and settled in this valley. Creeks like Adobe Creek have carried and continue to carry eroded material down from the mountains. As you walk to Station 3, keep your eyes on the freshwater marsh to your right for a Western Pond Turtle, which might be sunning itself on a clump of vegetation, log, rock, or shore.

Station 3 – Adobe Creek and Steelhead Trout

This is Adobe Creek. Had you stood here in 1982 you would have seen a dry stream bed, littered with trash and denuded of vegetation. Native fish populations, including Steelhead Trout, had dwindled. Steelhead are threatened due to several factors, such as sedimentation, loss of streamside vegetation, water diversions, obstructions to their migration, and deterioration of their spawning grounds. In 1984, the United Anglers of Casa Grande High School officially adopted Adobe Creek. Other agencies joined their efforts to restore Adobe Creek and its Steelhead population. The creek was cleaned up and trees were planted providing shade to lower the water temperature to the comfort zone of native fish populations. Measures to control erosion were implemented and water diversions were eliminated. Because Steelhead migrate to the ocean from the freshwater creek where they were born and return to the same creek to lay their eggs, a fish ladder was built near Adobe Road to aid fish traveling upstream. The pool on the lower side of the tree enshrouded rock wall (that crosses the creek near you) was created as a resting pool for fish to acclimate to the change in salinity when entering or leaving the creek. Station 4 is just on the other side of the bridge.

Station 4 – Restoring the Environment

Native vegetation has been planted along the footpath and banks of the creek. The lower portion of Adobe Creek, between the river and the rock wall, has been terraced to maintain a low gradient. The plantings along the creek, below the pool, were added to restore tidal marsh habitat. The land west of the creek, including Rocky Dog Park, is also restored tidal marsh which was diked and drained in the 1880’s to create land for agriculture. The levee was breached in the 1970’s when the city purchased the land. Once the levee was broken and the tidal water entered, the plants in this former agricultural field died, wetland plants returned, and animals adapted to a saline environment with the daily tidal flows. Restoration projects like this are undertaken in the hopes of returning ecological systems to their natural state.

Station 5 – Tidal Marsh

The rising and falling of the tides pose great challenges to marsh life. Not only are organisms exposed to varying degrees of moisture, but also changes in salinity and temperature. Lower marsh areas near the creek and river’s edge are home to only a few species of plants that can survive in very salty water: salt grass, cordgrass, pickleweed, gum plant, and sea lavender. These species have glands that excrete salt onto their leaves and stems where the salt can then be washed away as crystals or tiny sacs called vacuoles. In the autumn the vacuoles turn red and fall away. The excretion of salt allows the plants to survive in the presence of salt water that would kill most plants. Pickleweed is not only edible for humans but is also the main source of food for the endangered Salt Marsh Harvest Mouse. You can find examples of these plants along the creek in the adjacent marshes.

Station 6 – An Historical Perspective

Six to ten thousand years ago, the Coast Miwok Indians took up residence in this area. They became well adapted to using the land for food and shelter and yet lived so softly on the land that hardly a trace of their existence can be found. In 1830, Mexico, which still had control of California, feared Russian invasion and sent Mariano Guadalupe Vallejo here to build a fort, the Casa Grande, to help protect the area. His landing was near the top of a large meander of the river, at the end of Casa Grande Road, where the dog park is located. Native people were “hired” to help establish this huge estate. In 1837, smallpox killed most of the Native population. In 1852, more settlers moved into the area and “Newtown” was established at Vallejo’s Landing. The river, beyond the Landing, was deemed impossible to navigate. But soon it was found that steamers could travel further upstream. This allowed Petaluma to prosper and Newtown became history. In 1930 at the site where Newtown was born and died, a city landfill was developed. Active until the 1950’s as a landfill, it then re­mained unused until 1995 when it was capped in clay and earth, creating the dog park. As you walk to Station 7 look for signs of humans having lived here in the past. You may see chard and beet plants by the pond on your left along the trail or across Adobe Creek.

Station 7 – The Tidal Mudflat

The tidal mudflat is a specific kind of wetland lying between the vegetated marsh and the water’s edge that is alternately exposed and submerged by the rising and falling tides. A tidal mudflat can cover huge areas or be just a narrow strip of mud, such as along the river here. Tidal mudflats are rich with life. A double handful of mud can hold an estimated 40,000 live organ­isms. Most of these organisms are microscopic, but many kinds of tiny animals are visible, such as mussels, snails, worms, clams, and shrimp. Many of these burrow into the mud which protects them from water movement, enemies, and drying out. The more visible animals feed on the microscopic ones and in turn, are eaten by fish, birds, and mammals. When the tide is out, the mud-probing shorebirds and ducks flock to the mudflats in search of food. As you continue your walk, look for ducks in the river and freshwater ponds formed from rain, especially if it’s winter or early spring.

Station 8 – Dredging and A Seasonal Wetland

When it rains, the creeks carry sediment down from the surrounding mountains. At one time, sediments collected in the vast marsh land that covered this area. Most of those marshes were diked and land developed for farming and sediment now settles on the river bottom. Almost half of the total sediment comes up from San Pablo Bay on high tides. These sediments make the river shallower, less navigable and more prone to flooding. Due to this sediment buildup, the river must be dredged about every four years. The ponds in Shollenberger Park were created as a site to collect and settle the dredge spoils. The creation of the dredge ponds has contributed to a rich and varied wetlands ecosystem. The water in the ponds is mostly from rain, but saltwater and mud are added during dredging and seep up during high tides. A large lake in winter and barely a puddle or two in summer (except after a dredge cycle or very wet winter), makes these ponds seasonal, brackish wetlands. During the wet season, organisms such as fish, water birds, fairy shrimp, and microorgan­isms must secure shelter, find food, locate a mate, and reproduce. What do these animals do in the dry season? They die, become dormant in the mud, deposit eggs to be born when the next rains arrive, or migrate to another location.

Station 9 – History of The Petaluma River

The Petaluma River is a tidewater slough. This once modest slough, twisting and turning through salt marshes 14 miles from town to San Pablo Bay, made Petaluma the largest city in all of Sonoma, Marin, and Mendocino Counties throughout the 19th century. In 1860 Petaluma was flourishing as a city, but navigation beyond what is now Rocky Dog park was still difficult, due to shallow water, tight turns, and a narrow channel. Chinese laborers were hired to hand cut a channel through the meander to straighten the river. In 1862 and again in 1870, a steam excavator deepened, straightened, and widened the cut even further, allowing steamships to travel easily all the way to Petaluma. Petaluma became a hub to ship eggs and hay to San Francisco.

And in 1880 the U.S. Army Corps of Engineers dredged and widened the channel 50-feet wider (100 feet total) and 3-feet deep at low tide. In 1959 Congress declared the Petaluma tidewater slough a river. This designation from slough to river authorized periodic dredging by the Corps of Engineers to remove sediment which accumulates on the river bottom. It remains less expensive to haul materials by barge than by truck or train. Tourism is also a major factor for keeping the river navigable. As you continue to walk south, look west along the river at the boat docks. This is the site of Haystack Landing where the Haystack Railroad was built in 1864 and ran until the river became navigable to town. The line ran from the Landing to 2nd and B Streets, shuttling people and goods from steamers on the river to town.

Station 10 – Animals (Mammals and Reptiles)

Other than birds, wetland wildlife is not always seen. However, signs left behind by animals are usually much easier to find than the animals themselves. Signs may include tracks, tufts of fur or feathers where an animal was eaten, claw marks on the ground where an animal dug, food fragments like shells or bones where an animal fed, nests, burrows, beds, animal droppings (scat), or small trails. Dried mud is a good place to find tracks. The most common animals (excluding insects and birds) seen here include Botta’s Pocket Gopher, Black-tailed Jackrabbit, Gopher, and King Snakes, Western Fence Lizards, California Voles, and Western Pond Turtle. Due to the rapid destruction of wetlands, over 50% of the animals on the California endangered or threatened species list are found to be wetland-dependent. As you continue your walk can you find more signs of animal life?

Station 11 – Shorebirds and Migratory Use Of The Wetlands

The season will affect the number and kinds of birds you see today. There are several birds who live here all year. Some of the resident shorebirds are Killdeer, Black-necked Stilt, and American Avocet. A large flock of American White Pelicans resides here mostly in the sum­mer. Other birds migrate through here just to rest and find food as they pass on to other destinations. Some birds fly round trip from the Arctic Circle to Mexico, taking advantage of the abundance of water and food. The park is increasingly being used by geese, swans, and numerous duck species as a stop along their migratory flight. There must be a series of wetland habitats a day’s flight apart for the birds to safely reach their destinations. Due to this dependence on wetlands, migratory bird populations will decline even further if wetlands continue to be removed. As you walk to Station 12, look for two different black and white, long-legged, and long-billed birds. The Black-necked Stilt has a straight bill which it thrusts into the mud, red or pink legs, glossy black back, and white underparts. The American Avocet has an upturned bill which it swings side to side in the mud, blue legs, black-and-white above, white below, and a rusty head and neck during breeding season.

Station 12 – The Value of Wetlands

In the last 150 years, 90% of California’s wetlands have been drained or filled to support farmland or commerce. It is estimated that if the current rate of wetland “reclamation” continues, less than 10% of the original wetland areas of California will remain by the year 2010. The field between you and the wastewater ponds was once a tidal marsh that was diked and drained for oat hay production. The floods of winter 1998 breached the levees. This began the return of seasonal wetlands to the upper field and tidal marsh to the lower field. In 2004 Sonoma County’s Agriculture and Open Space with the Coastal Conservancy bought the land and deeded it to the City of Petaluma. Many functions and activities take place in wetlands, making them among the most productive and valuable ecosystems in the world. Wetlands absorb excess water from runoff to help prevent floods; provide resting places for migratory birds; provide a nursery for young wildlife; strain silt and debris; filter toxins from water; neutralize toxic substances like pesticides; provide food for wildlife and humans, and provide important habitat for nesting waterfowl and other birds. Keep your eyes on the field in front of you and you may see a Black-tailed Jackrabbit or a Northern Harrier with an obvious white rump patch and a flight pattern of flying low to the ground, tilting from side to side.

Station 13 – Wastewater Treatment Ponds

On the far side of the field before you, beyond the Blue Gum Eucalyptus trees, there are ten ponds covering 162 acres. They are oxidation ponds (so-called because of the oxygen that is added to the system to aid in the break­down of bacteria) and are part of the city’s wastewater treatment system. Between the eucalyptus trees and where you are standing, you can see in the distance polishing wetlands which are a component of the new Ellis Creek Water Recycling Facility and Wildlife Sanctuary, completed in 2009. Closer, and to the right, is Gray’s Tidal Marsh which was formed in 1998 when the levee was breached. To your left is a trail that connects Shollenberger and the Ellis Creek site. The purpose of the water treatment system is to remove the organic material and pollutants, leaving the water in a form that is safe to release into the environment. When wastewater leaves your home, it is piped to the wastewater treatment plant where it is biologically treated and piped to the oxidation ponds to be disinfected and recycled or released. The treated water meets the California Regional Water Quality Control Board’s standards and is released into the Petaluma River (in the winter only) or recycled for commercial use. As the population grows and water resources become scarcer, reclaimed water is expected to become an important source of water for urban, agricultural, and wildlife.

Station 14 – Storm Drains and Glory Holes

Storm drain systems include street gutters, catch basins, culverts, and pipes. Water runoff from the nearby business park goes through storm drains and enters the channel behind you. This rainwater flows north into a cattail and tule marsh, goes through another culvert under the Shollenberger gate road and then into Adobe Creek on its way to the Petaluma River. The rainwater running off roofs, gardens, sidewalks, driveways, and streets which may pick up sediment, fertilizer, oil, paint, pesticides, etc. and adds these pollutants into the creeks, marsh, and river which can destroy wetland ecosystems.

When the ponds become too full of dredge spoils, the excess saltwater drains through the cement culvert on your right (north) into the channel behind you and also goes to the Petaluma River via the Adobe Creek. The high salt in dredge spoils water that flows into the channel can be injurious to marsh plants and trees on the banks.

Wetlands are filled with abundant plant and animal life that are sensitive to pollution. A healthy stream ecosystem has a low level of pollutants, high oxygen levels in the water, and diverse populations of macroinvertebrates (organisms lacking an internal skeleton and large enough to be seen with the naked


Station 15 – Tule Plants

The cattails and bulrush (tule plants) need a year-long wet environment to survive, as this freshwater marsh provides. The organic ooze Petaluma Wetlands Alliance logo(detritus) that cattails are rooted in is rich in nutrients but contains no oxygen. Cat­tails have developed hollow tubes in their shoots and stem to allow them to transfer oxygen down to their roots underwater. Cattails have female flowers that look like cigars or a cat’s tail. The male part is the short spike growing out of the top of the female flower. Bulrush has small brown flowers that are in clusters on the side of the stem. Can you pick out the cattails from the bulrush? Cattails were used exclusively by the Native Americans. The leaves were used as thatch for houses; the fluff from the dry seed stalks as an absorbent for “diapers”; and the shoots, flowers, and roots used as food. Today Muskrats eat the roots, stalks, and shoots of the cattails; and the Marsh Wrens and Red-winged Blackbirds use the leaves to weave their intricate nests and the fluff to line them.

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