The Upper Las Virgenes Canyon Open Space Preserve (formerly known as Ahmanson Ranch) has been the setting of several high profile films, beginning in the Silent Era and continuing into Hollywood's Golden Age of the 1930s-1950s. During this latter era, the area was called Lasky Mesa after the huge mesa near the center of the property. Through several name changes and ownerships, this land was also the subject of one of Southern California's most controversial land use disputes, a seventeen-year-long debate that finally resulted in establishing the area as public parkland for generations to enjoy.

Lasky Mesa is situated northwest of Los Angeles on the west end of Victory Boulevard. It was originally part of the 113,009-acre Rancho San José de Gracia, also known as El Rancho Simí, which was conferred by the King of Spain in 1795 and again in 1821 to brothers Francisco Javier, Miguel, and Patricio Pico from Sinaloa, Spain. Following independence, Mexico affirmed Rancho Simi to José de la Guerra y Noriega in 1842, who then received a U.S. land title for the acreage in 1865. The huge ranch was used primarily for pasturing livestock such as sheep and cattle, and areas were later used for oil drilling. A portion of the original adobe house owned by de la Guerra was used for the Robert P. Strathearn home of 1893, located in present-day Strathearn Historical Park in the City of Simi Valley. The Rancho Simi adobe site is designated California Historical Landmark No. 979. In the late 1800s, de la Guerra sold the entire property to Thomas R. Bard, one of the most powerful men in Ventura and Santa Barbara Counties, who later became a Republican U.S. Senator from California (1900-1905). Bard formed the Rancho Simi Land and Water Company in 1887, and divided the Rancho into tracts for future residential development.

The proximity of the ranch's rolling hills and mesas to the fledgling movie industry in Los Angeles made it a prime location for filming. Jesse L. Lasky was a pioneer Hollywood film producer and a key founder of Paramount Pictures with Adolph Zukor. In 1913, Lasky and Samuel Goldwyn teamed up with Cecil B. DeMille to form the Jesse L. Lasky Feature Play Company. On October 10, 1914, The Moving Picture World Magazine reported "The Lasky Company has acquired a 4,000-acre ranch in the great San Fernando Valley on which they have built a large two-story Spanish casa which is to be used in 'The Rose of the Ranch' which has just been started. The new ground is to be used for big scenes and where a large location is needed. A stock farm is to be maintained on the ranch. It is planned to use 500 people in the story. There will be 150 people transported through Southern California for the mission scenes. The studio will be used for the largest scene ever set up, the whole state and ground space being utilized." Directed by Cecil B. DeMille, Rose of the Rancho (1914) tells the story of Esra Kincaid (Dick La Reno) who, having taken the Espinoza land by force, sets his sights on the Castro Rancho. U.S. government agent Kearney (J.W. Johnston) holds him off until the cavalry arrives and he can declare his love for the film's heroine, Juanita (Bessie Barriscale), the "Rose of the Rancho." Released by Famous Players-Lasky Corporation on November 15, 1914, Rose of the Rancho was the first movie to be filmed in the area later known as Lasky Mesa. Famous Players-Lasky returned to Lasky Mesa a few years later to film The Thundering Herd (1925), the screen adaptation of Zane Grey's novel, which starred Jack Holt and Lois Wilson. In the 1930s, the Buck Jones Production Company used Lasky Mesa as a backdrop for two of their B-Western entries, The Throwback (1935) and Silver Spurs (1936). Released through Universal Pictures, both films starred Buck Jones and Muriel Evans. During the same period, Warner Brothers visited Lasky Mesa for Michael Curtiz' The Charge of the Light Brigade (1936) and William Dieterle's Another Dawn (1937) starring Errol Flynn opposite leading lady Olivia de Havilland (in the former) and Kay Francis (in the latter). It was also during this time that a William Randolph Hearst Company owned the property and unsuccessfully drilled for oil.

In the late 1930s, George E. Barrett, Jr., a wealthy financier and landholder, purchased the Lasky Mesa property. The Barrett Ranch raised horses, allowed filming, and was used as a vacation retreat for Barrett and his family. According to his daughter-in-law Muriel Barrett, the ranch house that is on the property today was built by George Barrett around 1938. Barrett apparently loved the unobstructed 360-degree view from the house that looked over the then rural San Fernando Valley and points south, west and north. The only trees on the property were the native oaks that still stand today. Barrett also owned vast holdings in Malibu. Through the late 1930s and 1940s, a number of bigger budget, partially historic movies were filmed at the ranch including Gone with the Wind (1939), Santa Fe Trail (1940), They Died with Their Boots On (1941), Duel in the Sun (1946) and Adventures of Don Juan (1948). In GWTW, Lasky Mesa was the film locale for the sunrise scene when Scarlett (Vivien Leigh) vows to never go hungry again. In 1949, R.E. Crummer bought Barrett's Malibu and Calabasas holdings, which included the land later known as the Ahmanson Ranch property. With the change of ownership, filming at the ranch steadily declined. During the 1950s, film production at Lasky Mesa was limited to The Homesteaders (1953) starring Wild Bill Elliott and Robert Lowery, and Wild Heritage (1958) starring Will Rogers, Jr. and Maureen O'Sullivan.

In 1963, Home Savings of America, a subsidiary of H.F. Ahmanson & Company, purchased the property with plans to build a residential subdivision. This first attempt at development, however, fizzled out quickly. More than twenty years later, in 1986, the Ahmanson Land Company was formed to create a master-planned community located atop Lasky Mesa and reaching out to the nearby hills and valleys. In 1992, public debate over development in the area intensified when the Ventura County Board of Supervisors approved a plan to create a sprawling, self-contained community consisting of 3,050 residences, two schools, two hotels, two golf courses, open spaces, and 400,000 square feet of commercial and business centers. In 1998, Seattle-based thrift Washington Mutual (WaMu) purchased H.F. Ahmanson & Company and its Home Savings of America unit for $9.9 billion. As a result of this takeover and those of American Savings Bank of Irvine and Great Western Financial of Chatsworth in 1997, WaMu became California's second largest bank. The acquisition also gave WaMu control over the Ahmanson Ranch, the hotly disputed undeveloped area northwest of Los Angeles. The fight against development, which began with Mary Wiesbrock and other local activists to preserve the entire property, quickly spread to include local, state and federal agencies, numerous elected officials, neighborhood associations, entertainment industry figures, businesses, lawyers, builders, grass roots organizers, scientists and environmental groups. Finally in 2003, after a seventeen-year heated debate, WaMu agreed to sell the ranch to the Santa Monica Mountains Conservancy (SMMC). The park purchase was made possible when funding became available from California's Water Security, Clean Drinking Water, Coastal and Beach Protection Act of 2002 (Proposition 50), the state bond measure approved by voters in November 2002. On November 7, 2003, the SMMC purchased the 2,983 acres, formerly Ahmanson Ranch, from WaMu in a simultaneous close of escrow with the Mountains Recreation and Conservation Authority (MRCA), securing the oak-studded pristine expanse at the southwest edge of Ventura County into parkland. The below-appraised-value sale price of $150 million was made up of a grant of $135 million from the State Wildlife Conservation Board, a grant of $10 million contributed by the State Coastal Conservancy, and $5 million from SMMC. No other park purchase in Ventura or Los Angeles counties has been larger in either land area or cost. The newly acquired public parkland (Ahmanson Ranch), which encompassed Lasky Mesa, was contiguous with and accessed from the existing 2,650-acre Upper Las Virgenes Open Space Park. This combined 5,633-acre public parkland was renamed Upper Las Virgenes Canyon Open Space Preserve. When it was formally dedicated on April 10, 2004, one of Southern California's most controversial land use debates finally came to a close, and this spectacular wild land was officially preserved for future generations.

The Upper Las Virgenes Canyon Open Space Preserve offers more than mere vistas of unspoiled California landscapes. Collectively diverse, its protected habitats are home to many endangered species such as the California red-legged frog, the San Fernando Valley spineflower, and the Southwestern willow flycatcher. Las Virgenes Creek, headwaters for Malibu Creek, originates at the park. As it flows through the valley, the water of Las Virgenes Creek disappears below the sands of the willow forest and reappears several times, creating pools that are an ideal habitat for amphibians. Crummer Canyon, an inter-mountain range wildlife corridor named for R.E. Crummer, originates from the southeast corner of the Preserve and is one of only two habitat linkages that connect the Simi Hills to the Santa Monica Mountains.

The Preserve is located in the Simi Hills and is part of the Transverse Mountain ranges of Southern California, which were created from tectonic interactions between the North American and Pacific Plates. The portion of the Preserve that is south of Bell Canyon comprises Miocene sedimentary deposits of the Modelo Formation, which geologists date to between 5 and 24 million years ago. The northwestern portion of the Preserve in the upper Las Virgenes Creek valley is comprised of late Cretaceous sedimentary deposits of the Chico Formation, dating back to 145 million years ago. Two Native American tribes inhabited the Preserve in Paleolithic times. Although the territory was the domain of the Chumash people, it was considered part of a boundary area also shared by the Tongva. Chumash settlements in the proximity of the park included El Escorpion (near Bell Canyon), Shimiya (present day Simi Valley), Talepop (near Malibu Creek State Park), and the large coastal village of Humaliwo (present day Malibu). The village of Huwam is significant because, prior to European contact, it was a multi-cultural community where Chumash, Tongva and Tataviam peoples lived and interacted with one another. Kas'elew (Castle Peak), a large rocky mountain on the property of Bell Canyon Park, is the reported site of this village. Although Castle Peak is located in Los Angeles County and is therefore not part of the Preserve, it has traditionally been an area of great ceremonial importance for the Chumash people. Priests and astronomers traditionally used it during winter and summer solstice ceremonies. Castle Peak is also significant because it represents one of the nine alignment points located within Chumash territory. The Preserve's vast grasslands, oak woodlands, streams and pools provided abundant hunting and foraging for native inhabitants.

The California State Legislature established the Santa Monica Mountains Conservancy in 1980 and thanks to its efforts, the vast expanse of rolling hills and mesas of the Ahmanson Ranch are being maintained for generations to enjoy. Centuries-old Valley Oaks dot the countryside and sycamores line the canyons of this landscape that the entertainment industry once used as a backdrop for several of their film productions. The Conservancy has helped to preserve over 55,000 acres of parkland in both wilderness and urban settings, and improved more than 114 public recreational facilities throughout Southern California. Today, many of the beautiful lands bought by George E. Barrett, Jr. as investments are now protected parkland, including Lasky Mesa, Cheeseboro Canyon to the west, parts of Point Dume, Escondido Canyon, and Latigo Canyon in Malibu.

The Upper Las Virgenes Canyon Open Space Preserve can be accessed from two trailheads. The San Fernando Valley access to the Preserve is via the aptly named Victory Trailhead located at the western end of Victory Boulevard in West Hills. The Calabasas access is at the Upper Las Virgenes Canyon Trailhead located at the northern end of Las Virgenes Canyon Road, approximately 2 miles north of Highway 101. The Preserve's interior can be accessed via several trails. El Escorpion Trail runs from Bell Canyon Park (managed by the City of Los Angeles, Department of Recreation and Parks) south and then westward to connect with East Las Virgenes Canyon Trail. The Mary Wiesbrock Loop Trail, named in honor of the activist, encircles the southern edge of Lasky Mesa. The trails are open to hikers, mountain bikers, and equestrians, who are free to explore multiple routes throughout the Preserve from either the Victory or Upper Las Virgenes Canyon Trailheads.