VASCULAR PLANTS OF UPPER NEWPORT BAY
OVERVIEW OF THE SOILS IN AND AROUND UPPER NEWPORT BAY
AS COMPILED BY ROBERT DE RUFF
The purpose of this paper is to determine the soil types exposed around the Upper Newport Bay Estuary and to describe these soils based on my observations and tests of the 150+ samples taken around the bay. My interest relates to the soils as a planting medium for the existing plants found around the Upper Bay more than the geologic history of the samples.
All soil samples were observed under a microscope where the grain size was clearly evident, however this information would be difficult to obtain in the field and my intent is in how to determine soil information in the field. Samples were not screened for percentages of material passing a given screen, a slow and tedious process that would not have added much to my knowledge of the soil as a planting medium and would not have been possible in the field. The final analysis of each sample consisted of breaking the small clods that form when the dry material is dug up or has dried after taking a moist sample. I found that for my purposes a description of the soil, including the difficulty of breaking a small clod with the fingers gives an accurate indication of the amount of fine material in the sample. The more fine material there is, the harder the clods are to break because the fines tend to bind the larger soil grains together.
I checked the pH of each soil sample and find that most of the samples are neither alkaline nor acidic and have a pH of about 7.0. The most acidic sample tested was about 4.0 with no other tests even in the 5 range of acidity. This test was rerun with the same results and another location several hundred feet away also tested near 4. The most alkaline sample was a little over 8.0. pH tests for individual plant locations were not done originally and it would be impossible to go back and check them now but I have given the pH range of the nearest tested areas for most plants in the study.
The bluff sides around the Upper Bay are mostly dry and rely on rainfall to support plant growth. There are a few notable exceptions to the dry bluff sides and one is along the bluff below Eastbluff North where there are several seepage areas. The extra water supply there has allowed trees to grow and under the trees several species are found that occur nowhere else in the Upper Bay. At one location, near the base of the Back Bay Drive hill up to Eastbluff Dr, there is a filled draw that had so much seepage that it was finally channeled under Back Bay Dr. Before the seepage water was piped under Back Bay Dr. there were a number of freshwater plants that grew along the edge of Back Bay Dr. some were not found elsewhere in the Upper Bay.
The variety of plants found on the bluffs surrounding the bay is remarkable and is split about half to native plants and half to non-native plants.
The oldest geologic formation exposed around the Upper Bay is the Monterey Formation which was laid down during the period from 16-10 million years ago. The Monterey Formation is diatom rich shale, with particles too fine grained to be visible to the naked eye. The white cliffs visible in the southern part of the Bay are Monterey Formation. The Monterey Formation also contains clays, widely spread organic matter and occasional interbeds of mudstone.
The formation overlying the Monterey is the Capistrano Formation which was laid down 10-5 million years ago. It is composed of sediments, predominately mudstones and sandy siltstones. In the Upper Bay, the boundary between the Monterey Formation and the Capistrano Formation has been mapped at the mouth of Big Canyon. The lighter colored cliffs to the south of Big Canyon are Monterey Formation and the brown colored cliffs to the north are interpreted to be the Capistrano Formation.
Overlying the Capistrano Formation is a shallow marine deposit laid down between 5 and 2 million years ago and composed of light brown, fine to coarse grained sandstones and siltstones. This formation is called the Fernando Formation. The line of demarcation between the Capistrano and Fernando formations is not as easily seen as the line between the Monterey and Capistrano formations but it is mapped at about the 23rd St. area on the westerly side of the Bay and the southerly end of the Eastbluff burn area on the easterly side. On the easterly side of the bay the southerly end of the burn area is marked by a gravel road leading from Back Bay Dr. to the bluff top. The terms 23rd St. and burn area are better defined in the sub-area descriptions found elsewhere in the plant study.
The top of the San Joaquin Hills first emerged above sea level 1,230,000 years ago. As the coastal areas were uplifted, wave action cut several horizontal benches into the sedimentary rocks along the coast. The benches were covered with younger sediments called terrace deposits. Six marine terrace benches have been identified in the San Joaquin Hills, ranging in age from 125,000 to 500,000 years. The last terrace formed is in part the flat area around the Upper Bay.
Fifty Thousand to 120,000 years ago the terraces surrounding the Upper Bay were raised above sea level and they soon began to support terrestrial plant life. For thousands of years since rising above sea level the plant life has lived, died, dropped leaves and fruit and this coupled with chemical changes and weathering has formed the top soil as we know it today.
The ice age 17,000 years ago caused a drop in sea level of as much as 300 feet below the present level and the rivers of the various canyons continued to cut deeper as the coastal hills were raised higher. The rainfall during and after the ice age that ended about 10,000 years ago was much higher than it is today, possibly as much as 80 inches per year, allowing the rivers to cut deeper into the sediments forming canyons well below present sea level. Bedrock in the Upper Bay today is up to 120 feet below the present ocean level and alluvial materials carried by the water courses that feed the bay and by landslides and alluvial materials off the sides of the bluffs have filled the Upper Bay to its present level.
The youngest geological deposits found in the Upper Bay are the unconsolidated sediments found in the bay today and called Quaternary Alluvium. Quaternary refers to the time period from 2 million years ago to today. The Quaternary sediments most visible today were dredged from the bay into marshy inlets at Northstar Beach, 23rd St, lower Big Canyon and on one marshy island which is now called Shellmaker Island. The dredging was done by Shellmaker, Inc. from the late 1930’s into the 1970’s and its purpose was to collect shell from the sediments and sell it as a source of calcium carbonate to chicken farmers.
There are differing opinions as to what water source carved out the Upper Bay; some say the Santa Ana River cut the Bay and others say that with increased ice age stream flow San Diego Creek and the Delhi Channel could have produced enough flow to do the job. It is beyond the scope of this paper to speculate on which theory is correct.
Where the ancient formations are exposed, the bluffs are generally very steep and constant minor slippages prevent most growth there. Where the bluffs are flatter, topsoil and terrace deposits have covered the ancient formations and are the present day soil that most of the bluff-side plants grow in. The consistency of this soil mix is interesting, it varies from coarse sand with no silt to sand with heavy silt but there is no clay and with one exception described below none of the sand has large grained material exceeding +/- 2.0 mm. in diameter.
On the floor of the Upper Bay area, the Quaternary Alluvium supports the halophyte populations and is mostly inundated at the highest tides.
Northstar Beach, the 23rd St. lower terrace areas, The lower Big Canyon Quaternary Alluvium has been disturbed by the digging of a freshwater pond and by slippage from the Monterey Formation on the southerly side. Because it has water from the subdivisions upstream, the heaviest growth of all the dredged Quaternary areas is in Big Canyon. All of these areas support sparse Coastal Sage Scrub and grassland. With a water supply as at Big Canyon, trees have grown in the Quaternary soil. Shellmaker Island produces the least growth and a test of its soil some years ago showed no nutrients at all in the sand there. Northstar Beach is today graded every year so there is almost no growth on the Rowing Center side of the freshwater creek. At one time this same area produced a plant cover consisting of a number of species including, Camissonia cheiranthifolia ssp. suffruticosa, Lotus scoparius and Heterotheca grandiflora. The list of plants found at Northstar Beach is long and varied and is described in the plant data sheets. The floor of the 23rd St. area is in at least two levels, the lowest being composed of dredged Quaternary Alluvium and the upper being a soil which is consistent with the surrounding area. The area has seepage from the land across Irvine Ave. which makes a portion of the lower elevation land soft and marshy. The wet area nearest Irvine Ave. supports cattails while the area nearer the Bay supports Juncus acutus and other salt marsh plants.
As noted above, the bluff side soils around the bay fall into the broad category of coarse sand to fine sand with considerable silt. There were a few anomalies that I found and I relate them here for interest only. On the westerly side of the bay at the highest point above the northerly side of the 23rd St. bench are small outcroppings of an almost black soil with many shells. This outcropping is covered with a layer of terrace deposit so its extent is impossible to determine without borings. This same formation occurs across the bay on top of the northerly side of Newporter Canyon at its westerly edge. The relationship of this formation to the terrace deposits is unknown.
Another anomaly occurs on the northerly side of Big Canyon where the transition from Monterey Formation to Capistrano formation takes place. Here, there is an exposed layer of very hard rock, so hard I could not get a knife tip to make a mark in it. I assume that the rock is mudstone. Going northerly along Back Bay Dr., the rock layer is visible intermittently along the bluff-side for several hundred yards, where it finally disappears.
The northerly portion of Shellmaker Island is separated from the Fish and Game Headquarters and the new Science Center by a channel. This portion of the island is covered with sparse plants and grass except for one location where there are willow and other small trees. Willow trees require fresh water, so where on this dry island surrounded by salt water does the fresh water come from?
Finally, and the most interesting anomaly I have found is an ancient stream channel filled with loose conglomerate material lying about 15 feet below the present mesa. The location of this old channel is on the westerly side of the bay near a vertical bluff that faces the Delhi Channel before it curves around the old Salt Works dike. The interesting question is how did the old channel get cut and filled with conglomerate material unless the land was above sea level at some time before the marine terrace deposit was laid down? What was the source of the conglomerate material, it had to come from somewhere higher than the present mesa elevation?
It is hoped that this short summary of the Upper Bay soils may be of value to others studying the flora of Upper Newport Bay.
© 2010 ROBERT DE RUFF