The Pajaro River ( is bird in Spanish) is a U.S. river in the Central Coast region of California, forming part of the border between San Benito and Santa Clara Counties, the entire border between San Benito and Santa Cruz County, and the entire border between Santa Cruz and Monterey County. Flowing roughly east to west, the river empties into Monterey Bay, west of Watsonville, California.
History The first European land exploration of Alta California, the Spanish Portolà expedition, camped near the river for two nights, in the vicinity of today's community of Watsonville, on October 8–9, 1769. The party continued north the next day toward Santa Cruz. Expedition soldiers called it "Pajaro" (meaning "bird" in Spanish). Franciscan missionary Juan Crespí, traveling with the expedition, noted in his diary that they "found half the body of a very large black bird, hanging [from] poles" (possibly a condor).
The Pajaro River has had many names. Early Spanish maps had the name and . Alternate names included Pigeon River, , , , San Antonio River and .
In 1953 the State Water Resource Control Board determined that the Pajaro Valley Watershed suffered from saltwater intrusion due to groundwater overdraft. In the 1970s, the groundwater basin consistently fell below sea level, and was identified in 1980 as critically over-drafted. By the 21st century, 54 square miles of the Pajaro Watershed's groundwater supply was overdrawn and as a result, below sea level making the area susceptible to saltwater intrusion.
Flooding The Pajaro River has a recurring history of flooding. The towns of Pajaro and Watsonville were built on the river's natural floodplain. Before the Army Corps of Engineers built the levees, flooding devastated homes, businesses, and agriculture. Since the $748,000 levees were constructed in 1949, there have been several instances of flooding from severe weather events and failed levees. In 1963, the USACE (United States Army Corps of Engineers) acknowledged poor planning in levee design, and congress authorized re-construction of the flood control system, however no funds were provided from the federal government.
Following the 1995 floods, several lawsuits were issued against the different counties and cities by farmers and homeowners affected. Santa Cruz County, Monterey County, and the California Department of Transportation were all held responsible for failing to maintain the Pajaro River during floods and sued by about 250 people. Plaintiffs held the counties responsible because in 1944, both counties made promises to maintain the levees implemented by the Army Corps of Engineers.
Timeline DateFlooding impacts1890A severe flood was enhanced when a rail bridge's pilings by the mouth of the river allowed for debris to accumulate and cease discharge to the ocean. As a result, the floods were remembered as the "Highest yet known" for the next 50 years.1894Flooding near the city of Watsonville, California1907Major flooding region wide.1911Each year experienced overflow near the city of Watsonville.191419151916192219271931193319371938Flooding1949(Army Corps of Engineers levee construction)1955Flooding1963Overflow near the city of Watsonville.1982Flooding of agricultural land at Llagas Creek at the Pajaro River bordering Santa Clara and San Benito Counties. Floodwaters at the confluence of Pajaro River and Carnadero Creek flooded agricultural lands in Santa Clara and San Benito counties. The Pajaro River inundated part of Watsonville and adjacent agricultural land. High stages in the Pajaro River blocked Watsonville drainage.1983Flooding in agricultural lands at the confluence of Pajaro River and Carnadero Creek.1986Significant flooding on the Pajaro River in February.1995All residences and businesses damaged; 2,500 evacuations
Damage to 3,280 acres of agricultural crops along the Pajaro River were estimated at $67 million, and urban damages in Pajaro estimated at $28 million. Two persons drowned1997Flooding1998Town of Pajaro evacuated. The levee along the Pajaro River was breached in several places, and a Presidential disaster was declared.2005Town of Pajaro is flooded. Evacuation orders were never given until the flooding started. Resulting in stranded citizens. And much more unneeded loses.2023Town of Pajaro evacuated to surrounding shelters the following day. The levee along the Pajaro River breached at midnight on March 10 due to ongoing storms in the region and poor levee conditions.
Geology
The San Andreas Fault line crosses the Pajaro River at the Pajaro Gap just east of Chittenden Pass and Logan, California (near Aromas) on California State Route 129. The Salinian Block rests above the Pacific Plate which slips north along the San Andreas Fault. It is made up of granitic material, and marine sediments.
The Pajaro River has a history of changing its course due to the San Andreas fault slippage between the Pacific plate and the North American Plate. At another time it flowed into the Elkhorn Slough in Moss Landing, California, then into the Pacific Ocean, but today it joins with Corralitos Creek to discharge into the Pacific at a slightly more north location.
The 1989 Loma Prieta earthquake in the Santa Cruz Mountains deformed the Pajaro levee system.
Other faults within the watershed are the Zayante fault, Sargent Fault, and Calaveras fault.
A. R. Wilson Granite Rock quarry is located by the Pajaro gap adjacent to the river in San Benito County.
Geography Due to the geology in the area, the geomorphology of the watershed is unique. The river begins at Diablo range in the east. In the south, from the Gabilan mountains flows another tributary northward. From the north, tributaries flow from the Santa Cruz mountains southward to meet with the Pajaro.
Climate The climate of the region is Mediterranean. Watsonville annual high temperatures reach and lows of . The average temperature is around and average annual precipitation (essentially all in the form of rainfall) is about .
Certain tributaries frequently run dry due to a lack of rainfall in the summer.
Watershed The watershed is approximately and covers portions of Santa Cruz, Santa Clara, San Benito, and Monterey Counties. The Pajaro River mainstem begins just west of San Felipe Lake, also called Upper Soap Lake, which is a permanent natural lake formed by the confluence of Pacheco Creek, Tequisquita Slough and Ortega Creek. Pacheco Creek's headwaters are in the Diablo Range at about elevation. The Pajaro River mainstream flows west for 30 miles (50 km), passing the city of Watsonville and emptying into Monterey Bay. Lower Soap Lake, also called Soap Lake, is an intermittent body of water a few miles downstream of the upper lake. This type of water body forms when the channel below is unable to keep up with the flow coming from upstream. The San Andreas Fault divides the watershed and is responsible for altering historical flow paths.
Upper watershed San Felipe Lake lies just south of the Santa Clara County line in San Benito County, just south of Highway 152 east of Gilroy at the foot of the Diablo Range. The lake is a sag pond dammed by the fault scarp of the Calaveras Fault, which forms a natural dike along the western shoreline. It is perennial in all but the driest years, e.g. 1977. San Felipe Lake used to be 50% larger until the man-made North and South Outflow canals, which drain to the Miller Canal, were cut through the western rim in 1874.
The Pajaro River's largest tributary is the San Benito River which is much longer than the Pajaro, flowing northwest from its source at an elevation of on San Benito Mountain on its course between the Diablo Range and the Gabilan Range, traveling for about before its confluence with the Pajaro River, about upstream from the ocean. The lowest tributary of the Pajaro River is Salsipuedes Creek which drains the Corralitos Creek and Salsipuedes Creek sub-basins.
Lower watershed The lower watershed is in Santa Cruz and Monterey Counties which currently have levee systems. The original river system was Corralitos Creek, fed by Aromas Creek. The Pajaro river has taken over this system, and Corralitos Creek is now only a tributary.
A residential development, agricultural fields, and Zmudowski State Beach border the Pajaro River mouth and the connecting Watsonville Slough. The river mouth is often open to tidal action for extended periods, especially during the winter months. Should the mouth fill with sediment, it must be physically reopened to prevent nearby agricultural fields from flooding.
The main water source for agriculture and drinking water in the region comes from groundwater. The three primary aquifers in the Pajaro Watershed are the Alluvial, the Aromas, and the Purisma aquifers. All three suffer from seawater intrusion due to groundwater overdraft, the worst affected being the Aromas aquifer. The Alluvial aquifer is heavily polluted by agricultural runoff.
Water quality The river is heavily polluted by people dumping illegally. One cleanup in 2015 revealed over 1,000 tires, five boats, two trucks, and tons of trash.
High toxicity levels in the river are a result from agriculture in the watershed. During low flows, organophosphate pesticides have been detected in the river, and organochlorine pesticides have been detected post-high surface runoff events. Toxaphene, DDT, and Diazinon have also been detected at concentrations unhealthy to local aquatic species.
Ecology In 2006, the Pajaro River was designated as "America's Most Endangered River" by the American Rivers organization, "due to levees" constructed by the Army Corps of Engineers along its lower and severe runoff into the river from agricultural fields.
There are six species listed as threatened or California species of special concern (SSC) under the CESA that regularly occur and/or breed near or in the Pajaro River. Western pond turtles (Actinemys marmorata), pallid bat (Antrozous pallidus), burrowing owls (Athene cunicularia), dusky-footed woodrat (Neotoma fuscipes), least Bell's vireo (Vireo bellii pusillus), and the yellow-breasted chat (Icteria virens). Four species are listed as threatened or endangered under the federal Endangered Species Act of 1973 (ESA) that are present or for which suitable habitat exists in or adjacent to the Pajaro River. Steelhead trout, the California red-legged frog (Rana draytonii), the Northern tidewater goby (Eucyclogobius newberryi,), and the snowy plover (Anarhynchus nivosus), which nests at the Pajaro river mouth at Zumdowski State Beach at the Pacific Ocean.
Native California fish present in the lower Pajaro River are: three-spined stickleback (Gasterosteus aculeatus microcephalus), Sacramento perch (Archoplites interruptus), riffle sculpin (Cottus gulosus), Russian River tule perch (Hysterocarpus traskii traskii), South Central California Coast steelhead trout (Oncorhynchus mykiss), and thicktail chub (Siphatales crassicauda).