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Megaflood & Megadrought - How They Changed Contra Costa

Pacheco was once an important inland shipping port for central Contra Costa County. The idea of a major shipping port located six miles inland on Walnut Creek (once known as Pacheco Creek) is for many a fantastic leap of imagination. Today Walnut Creek is a concrete flood control channel that, for most of the year, carries shallow runoff from lawn watering suburbanites and occasional winter storms.

Pacheco is now a sleepy, unincorporated slice of Contra Costa County wedged between Martinez, Pleasant Hill and Concord. However, during the 1850’s and 1860’s, Pacheco was the county’s bustling commercial center. It was the shipping port for the grain grown in the Ygnacio, San Ramon and Tassajara valleys. Warehouses, a flour mill and shops grew up along the creek. Walnut Creek then flowed deep and free into Suisun Bay. For over 20 years, from 1851 to nearly 1873, Pacheco was a major shipping port for central Contra Costa County. This essay is a description of how both Nature and Man combined forces to change the history of Contra Costa County.

The destruction of Pacheco’s Walnut Creek shipping channel occurred gradually over many years and for many reasons. It is an environmental detective story with clues in the historical and geologic records. A complex series of natural events combined with man-made ecologic damage eventually ruined Pacheco's growing prosperity.

In 1828 a grant of nearly 18,000 acres was made to Salvio Pacheco for his services to the Mexican government. He occupied his Monte Del Diablo land grant in 1834 (9). The Salvio Pacheco rancho stretched from Mt. Diablo to the Sacramento River. The Martinez, Moragas, and Welch families also obtained land grants covering most of central Contra Costa County. These large cattle raising operations had unforeseen ecologic consequences. Heavy cattle grazing soon destroyed the native grasses setting in motion further changes to the land.

In 1851 American settlement started in the Ygnacio Valley. Wheat, oats and barley were important crops by 1852-53. In 1854 twenty-five Ygnacio Valley farms were shipping their grain from the Pacheco embarcadero down Walnut Creek to San Francisco (6). Within a couple of years most of the central Contra Costa farms were sending their grain to Pacheco. Initially sailing craft of up to 100 tons traveled six miles up Walnut Creek to take on cargo at Pacheco (9). Eventually even small stern wheelers steamed up Walnut Creek to load grain for the San Francisco market.

During the 1850’s warehouses were constructed at Pacheco to handle the growing grain shipments from the Ygnacio, San Ramon and Tassajara valleys (6). The firm of Lathrop, Fish & Walrath built the first grain warehouse at Pacheco in 1853. Later George Loucks owned the building (8). An additional warehouse was constructed in 1857. A flour mill was built on the creek alongside the warehouses. In 1860 Mr. Fassett with Dr. Carrothers purchased land from Salvio Pacheco near the shipping port and laid out city lots for Pacheco, a growing settlement with a bright future (9).

Wheat growing and cattle raising was not the only important economic activity in Contra Costa. In 1850 Frank Such and W.E. Whitney began quarrying limestone from Mt. Diablo's foothills. The limestone was converted to lime to make the mortar needed to build San Francisco and Stockton. The lime was shipped down Mt. Diablo Creek, a tributary of Walnut Creek (6). On the bank of Mt. Diablo Creek, Frank Such built the kilns that turned limestone into lime. Three thousand barrels of lime a month were shipped down Mt. Diablo Creek and Walnut Creek from 1850 through 1862 (9).

During the 1850’s Mt. Diablo Creek flowed the year round. Small sailing craft traveled up the Walnut Creek slough and entered Mt. Diablo Creek to load their cargoes of lime. Sometime before 1881 Mt. Diablo Creek was filled with mud and silt (9). What could have been the causes of this environmental disaster?

As noted earlier in this essay, major changes to the environment began with the introduction of large-scale cattle raising into Contra Costa County. Native bunch grasses were driven to virtual extinction by overgrazing (2). The delicate native grasses were replaced by more rugged wild oats, mustard and ripgut, all foreign imports. Wild oats evolved in southern Europe alongside domestic cattle and were genetically equipped to handle the grazing pressure from large cattle herds (10). Intense, large scale cattle grazing of native bunch grass during California’s dry summers quickly killed off most of the sensitive native grasses. The shallow rooted wild oats responded to overgrazing by replacing the deeply rooted, native bunch grasses (12).

Cows that before the gold rush sold for four dollars a head, sold for as much as 500 dollars a steer in 1849 (5). Cattle herds were driven from Mexico, Texas and the Middle West to California to satisfy the demands of the expanding mining camps. A pre-gold rush population of half a million head of cattle quickly exploded to over three million (2) (5) producing dramatic overgrazing on California's cattle ranges. Whatever grass the cattle did not eat, the millions of introduced sheep devoured (5). Mutton as well as beef became staple meats of the ravenous gold camps.

Native bunch grass’ deeply rooted, large, matted root system absorbed the heavy winter rains and slowly released more moisture into the county's water table (12)(13). The smaller, shallow root system of the wild oats allowed faster runoffs during the winter rains. The loss of the native bunch grass resulted in increased erosion of Contra Costa’s hillsides, dumping more sediment into Walnut Creek and its tributaries.

Another environmental blow came in the 1850’s with the clear cutting of the redwood forests blanketing the headwaters of Las Trampas Creek, an important tributary of Walnut Creek (12). The rapid growth of San Francisco created an intense demand for lumber. By 1860 the redwood forests were gone. Even the giant stumps were removed for firewood. Now the winter rains and moisture laden fogs were not captured and absorbed by the forest. Heavy rains falling on Contra Costa’s coastal hills were no longer slowly released into Contra Costa’s groundwater system.

Clear cutting of the redwood forests, extinction of the native vegetation and overgrazing led to larger runoffs producing increased erosion, debris flows and landslides (12). During the 1850's, factors gradually increased the sediment load of central Contra Costa's stream system and setting the stage for what was coming.

The next natural environmental disaster was unprecedented and unexpected. California was hit with a Megaflood (3). In early November 1861 the normal winter rains began. But then it continued to rain through November. By December 9th the Sacramento Bee editorialized about the "Deluge of 1861.” The Union troops stationed in Stockton moved to Benicia to escape their flooded camp (7). Yet the rain continued to fall all the way through December. Rivers overflowed their banks and the San Joaquin Valley began to flood. Hundreds of thousands of cattle drowned. Thousands of people perished (3).

But the worst was yet to come. Heavy rains persisted through all of January 1862. When the rains finally ended, San Francisco records show that the city had received around 50 inches. Certainly on Mt. Diablo and the Berkeley Hills equal or greater rainfall occurred. Martinez received 49 inches. In Contra Costa it rained 15 inches in one week. All the county bridges were gone. The mining facilities at Nortonville and Somersville were washed away. At Sonora in the Sierra foothills over 8.5 feet had fallen by February 1, 1862 (1). In the Central Valley a lake 300 miles long and 20 to 60 miles wide formed (1). One could have boarded a steam ship in Bakersfield and sailed to San Francisco. So much rain had fallen that San Francisco Bay became a freshwater lake (3).

On the newly exposed hillsides of Contra Costa, stripped of its native grasses and redwood forests, the overwhelming winter rains proved disastrous. The unprecedented runoff eroded millions of tons of soil from the Walnut Creek watershed. Annie Loucks reported that after the flood, Walnut Creek began to silt up (8). Business records reveal the effect on Walnut Creek. After the megaflood of 1861-62, cargo ships could no longer reach Pacheco’s wharves. George Loucks was forced to move his warehouse three quarters of a mile downstream due to the rapid upstream filling of Walnut Creek (6). The megaflood of 1861-62 flooded Pacheco sweeping away warehouses and homes. But now an even worse disaster was about to begin.

In California a wet winter rainy season is commonly followed by drought. This time was no exception. After the extreme megaflood of 1861-62, there began such a horrendous three year megadrought from 1863 through 1865 that it permanently changed the economic face of California (11). For 1862-63 there was only 15 inches measured in San Francisco. Martinez recorded only around 9.5 inches. In Los Angeles only four inches were recorded. In the following years it was even worse. Los Angeles received only a trace of rain. A usually rainy San Francisco recorded only nine inches (12) (13). Given the current ratio of rain in San Francisco to rainfall in Contra Costa, most of central and eastern Contra Costa probably averaged less than four inches in 1863-64.

For the dry wheat farmers of central Contra Costa County, the drought years were devastating. Wheat was customarily sown from October until March and corn from March to July (9). But without moisture the winter wheat crop failed leaving the plowed fields dusty and barren.

The cattle industry in Contra Costa nearly vanished after three years of extreme drought (12). On California’s cattle range the stench of dead cattle filled the air (14). It became so bad that cattle were dying not only from starvation but from suffocation caused by dust inhalation (5). The over-grazed, drought stricken hills were stripped of their protective vegetation. In Southern California starving steers were sold for thirty-seven and a half cents apiece (14). By the end of the drought, over two and half million California cows had died. Crushed by debt, most of the remaining large ranchos were broken up and sold (11).

Normal rain fall returned in 1865 and 1866. In 1867-68 even heavier rains were recorded. Pounding drought damaged hillsides, rain water cascaded down the slopes turning gullies into deep ravines. This is a quote from the first history of Contra Costa County written in 1882 by Munro-Fraser (9). He begins by discussing two famous Contra Costa pioneers, Elam Brown and Nathaniel Jones, who arrived in the late 1840’s. Then Fraser goes on to note the changes to the Contra Costa countryside.

"The country in its general aspect has been greatly changed since their arrival, especially in the matter of ditches, many of these which now are of considerable magnitude, being then more drains. The prime cause of this we believe to have been the breaking of the upper crust of the soil by the trampling of stock, which increased in number year by year and consequently caused the greater damage as their hundreds were changed into thousands." (Page 427, History of Contra Costa County, 1882).

Less absorption of rain water meant greater erosion stripping the soil from the environmentally damaged hillsides. The filling of Walnut Creek accelerated after the megaflood of 1861-62 and the extreme drought of 1863-65.

During the rest of the 1860’s, continuing deposition of mud and silt into Walnut Creek and its slough made the navigation of cargo ships to Pacheco increasingly difficult. The intense winter rains of 1868 produced more terrible flooding of Pacheco. Faster runoffs and Walnut Creek’s gradual fill up of silt, mud and sand had reduced the creek’s water carrying capacity. Repeated floods and fires during the 1860's crippled Pacheco's prosperity (6)(8).

To add insult to injury, from 1852 to 1883 hydraulic gold mining in the Sierras poured huge amounts of sand, mud and silt down the Sacramento River and into Suisun Bay. Today these deposits are found as far west as San Francisco Bay (3). By the middle 1860's sand and silts formed shifting barriers in the entrance of the Walnut Creek slough making it increasingly difficult for ships to enter Walnut Creek (8).

In 1869 the offer of free or inexpensive land to the flood prone merchants of Pacheco by Salvio and Fernando Pacheco was warmly received. The site of the new settlement lay two miles to the east of Pacheco on higher ground. Many accepted the offer and the new town of Todos Santos (later Concord) was born (9). This was the final blow to the future of Pacheco. By 1873 regular shipments by boat had become nearly impossible because of the silting up of Walnut Creek. With the loss of the port and the decline in Pacheco's population, the Contra Costa Gazette publishers abandoned the town and moved to Martinez (6).

In the Old World this sad story of environmental damage and its consequences has been replayed many times. The great classic ports of Ephesus and Troy were abandoned after their harbors filled with mud and silt. Man’s destruction of native forests and overgrazing caused massive erosion and silting up of some of the great harbors of antiquity.

In summary Walnut and Mount Diablo creeks, two important commercial Contra Costa waterways of the 1850’s and 60’s, suffered the same fate and for many similar reasons. Overgrazing, extinction of the native grasses and destruction of Contra Costa’s first growth redwood forests made the Walnut Creek watershed prone to accelerated erosion and deposition. Together with additional catastrophes in the form the greatest rainfall in the West Coast's recorded history immediately followed by Californian's greatest drought ultimately doomed the navigability of Walnut and Mt. Diablo creeks and with them, Pacheco's commercial future.

(Note: the author is a geologist interested in the influence of geologic forces on human history.)


  1. Brewer, W. H., 1930, Up and Down California in 1860 - 1864, Third Edition, Francis Farquhar, editor, republished 1966, University of California Press.
  2. Dasmann, Rayond F., winter 1998/99, "Environmental Changes Before and After the Gold Rush", California History, vol. LXXVII, no. 4.
  3. Dettinger, Michael D. & B. Lynn Ingram, January 2013, "The Coming Megafloods," Scientific American, pages 64 - 71.
  4. Guinn, J.M., 1911, "From Cattle Range to Orange Grove," Historical Society of Southern California, Gilmore, Ray and Gladys, editors, 1966, Readings in California History, Thomas Y. Crowell Company.
  5. Jelinek, Lawrence, winter 1998/99, "Property of Every Kind: Ranching and Farming During the Gold-Rush Era," California History, vol. LXXVII, no. 4.
  6. Hulaniski, F.J., 1917, The History of Contra Costa County, The Elms Publishing Co., Inc., republished by the Contra Costa Historical Society.
  7. Levy, JoAnn, 2003, "Two Remarkable California Pioneers, Eliza Forham and Georgiana Bruce Kirby, California Territorial Quarterly, Winter Issue #56.
  8. Loucks, Annie, March 1939, "Early History of Pacheco," unpublished, 14 pages. Annie was born in Pacheco in 1858. Copy in the Contra Costa County History Society archives.
  9. Munro-Frasier, J.P., 1882, History of Contra Costa County, W.A. Slocum & Co., republished 1974, Brooks-Sterling Co.
  10. Preston, William, 1997, "Serpent in the Garden, Environmental Change in Colonial California," California History, vol. LXXVI, no. 2 & 3
  11. Robinson, W.W., March 1966, "Los Alamitos: The Indian and Rancho Phases," California Historical Society Quarterly.
  12. Rogers, J. David, 1988, "A Synopsis of the Development of Central Contra Costa County," Field Trip Guide to the Geology of the San Ramon Valley and Environs, Northern California Geological Society. (p.77)
  13. Rogers, J. David, 1988, "Pleistocene to Holocene Transition in Central Contra Costa County," ibid. (29)
  14. Romer, Margaret, April 1963, "The Story of Los Angeles - Part III", Journal of the West, vol. II, no. 2.

Bill Mero