The Spaniards introduced livestock grazing to the area. The introduction also brought European annual grasses to the area. The new grasses, more suitable for cattle grazing, replaced the native grasses of the area.

By the mid-1800’s the area around Rockville Park changed into many ranchlands and farms owned by European pioneers. In 1837, Chief Solano petitioned his ally General Vallejo, and the Mexican Governor Juan Alvarado, for a land grant called Rancho Suisun. His request was granted in 1842 and approved 1848. Chief Solano sold his land to General Vallejo. Spanish and American pioneers quickly settled the area.

33 American settlers attacked General Vallejo in Sonoma in 1846. During this time Chief Solano left the area. Ten years later, in 1856, Chief Solano returned to the area, dieing shortly after his arrival. His burial site is thought to be south of the park near Solano College. General Vallejo suggested the county be called “Solano.”

Rancho Suisun was sold by General Vallejo to Archibald Ritchie in 1857. Charles Ramsey, J.M. Baldwin, and Lewis Pierce owned sections of Rockville Park. The upper areas of the park were used for cattle grazing and woodcutting. Charles Ramsey owned “The Quarry” site of the park mining for concrete aggregate and stone. The stone used for local building gave the village Yul Yul a new name, Rockville

In 1932, the Pierce family sold several thousand acres in the area to the Mason family. The Mason family grazed cattle and built a stock pond from a natural spring wet meadow. Woodcutting continued on the property through the early 1960s. In 1966, the City of Fairfield began to acquire parts of the park.

At this time the City of Fairfield planned to develop Rockville Hills Park into an 18-hole golf course, restaurant, conference center, water slide, tram, and visitor center. The Lower Lake was created when a pump station was developed to water the golf course and for fire protection. In 1982 a ballot initiative was passed designating the land as an open space preserve. City ordinance now prohibits the construction of any new facilities in the park without voter approval. Grazing has continued in the park to this day as a means of fire prevention.