Although the California Office of Historic Preservation website lists this as marker #626, the number on the marker is actually #656.
The marker text reads as follows:
Adobe built about 1863 by A. S. Ensworth. Home of Capt. Rufus K. Porter and family. Curved timbers brought from the Clarissa Andrews, famed coaling hulk formerly of the Pacific Mail Steamship Co. Historian Hubert Howe Bancroft later owned this estate and here wrote a part of his monumental History of California.
From The Bancroft Ranch House Museum website:
The adobe house and surrounding grounds have a long history, mostly due to the presence of a nearby spring. This water source attracted people thousands of years ago to use the area. These people, the Indians presently known as Kumeyaay, left evidence of their encampments in the vicinity. The location name was transcribed by the Spanish as "Meti" or "Neti" and later changed to "San Jorge" in 1775 by the Spanish padres. The spring became known as "El aguaje de San Jorge" (Anglicized into "St. George's spring"). By the late 1830s the Indians had been removed from the area and herds of cattle and sheep grazed in the valley.
In May of 1863, Judge Augustus S. Ensworth, of San Diego, filed claim to 160 acres of land that included the spring. He built a two room adobe on the property, the first house erected by a white man in the eastern part of San Diego County. The wood used for beams and doorways was salvaged from the ship Clarissa Andrews, which had gone aground in San Diego Harbor.
Just before Ensworth's death, the ranch was sold to Rufus King Porter of San Pedro for $400. Capt. Porter, his wife Sophia, and daughter Rufina moved to the property on July 31, 1865. Rufus King Porter was the son of Rufus Porter, the founder of the Scientific American magazine, and he led a very colorful life holding numerous jobs and taking on various enterprises. He became well known for his columns about daily life, that appeared in several newspapers.
In 1866, at the urging of his daughter, Rufus renamed the area Spring Valley. In 1872, after the discovery by a scientist of a European snail (Helix aspersa) living on a nearby small mountain, Rufus named the prominent peak Mt. Helix. When, in 1885, the U.S. Post Office Department disallowed the use of two words for a post office name, Rufus submitted the name Helix and became the first postmaster in Spring Valley; the Helix Post Office operated out of his home.
In this same year, Hubert Howe Bancroft came to the area in search of a place to retire. He bought the Porter's ranch and also acquired neighboring ranches, accumulating around 500 acres. He called his property "Helix Farms." Over the next ten years, Bancroft hired workers to develop Helix Farms, planting orchards and building structures to run a ranch. A wide variety of trees and shrubs were planted including guavas, palms, olives, citrus, almonds, raspberries, blackberries, and currants. The adobe was too small to suit his family's needs when they visited the property in the summer months, so a house, known as "Cactus Cottage," was built on top of a nearby (cactus-covered) hill in 1889. Masons also constructed a "rock house" near the spring, where the children were taught. By the early 1900s, Helix Farms had become one of the largest olive ranches in southern California (many of the original olive trees can still be found in the surrounding area). Bancroft's son Griffing managed the farm since Hubert lived in San Francisco much of the time. Bancroft died in 1918 and after several years, his heirs sold the property. Much of it was subdivided into La Mesa Country Estates.
The adobe and 3.5 acres of land were purchased by the Spring Valley Chamber of Commerce in 1940. A wooden annex was built on the north side of the adobe and the building was used as a community meeting place. The Chamber was instrumental in getting the adobe designated California State Historic Landmark No. 626 in 1958, and it became known as the Bancroft Ranch House. By 1962, the deteriorating condition of the adobe required major restoration. Volunteers worked to reinforce it by bracing the walls, adding more support beams to the porch, filling in the cellar, and laying a concrete floor.
On March, 24, 1963 - just short of one hundred years after being built - the adobe was opened as a museum displaying artifacts of Spring Valley. The Spring Valley Historical Society was founded in April of that year and became the manager of the property, later purchasing the adobe and a portion of the land in 1967.