Rancho Arroyo de Las Nueces y Bolbones (also called "San Miguel") was a 17,782-acre (71.96 km2) Mexican land grant in present-day Contra Costa County, California given in 1834 by Governor José Figueroa to Juana Sanchez de Pacheco.
The grant was named after the principal waterway, Arroyo de los Nueces (walnut creek) and for the local group of indigenous Americans (Bolbones). The grant was on the western slope of Mount Diablo and includes the present day city of Walnut Creek. Approximately a quarter of the original rancho is now in the Mt. Diablo State Park.
Juana Lorenza Sanchez de Pacheco (1776-1853) was the widow of Miguel Antonio Pacheco (1745-1829). Miguel Pacheco, a soldier, was the son of Juan Salvio Pacheco (1729-1777) and Maria Carmen del Valle, who came to San Francisco in 1776 with the De Anza Expedition. The Pacheco family used its land for grazing cattle, but did not settle on the rancho.
With the cession of California to the United States following the Mexican-American War, the 1848 Treaty of Guadalupe Hidalgo provided that the land grants would be honored. As required by the Land Act of 1851, a claim for Rancho Arroyo de Las Nueces y Bolbones was filed with the Public Land Commission in 1852, and the grant was patented to the heirs of Juana Lorenza Sanchez de Pacheco in 1866. The grant was for two leagues (approx. 8857 acres; see Spanish customary units), but was confirmed for nearly four leagues (approx. 17,714 acres or 28 square miles).
Rosa Maria Pacheo, daughter of Miguel Antonio Pacheco, married Jose Maria Sibrian (1798 - ), and their two sons, Jose Ysidro Sibrian (1821 - ) and Jose Ygnacio Sibrian (1822 - ) inherited the rancho. Ygnacio Sibrian, the namesake of the Ygnacio Valley, built the first roofed residence in the valley around 1850. Shortly before John Marsh of Rancho Los Meganos died in 1856, Ygnacio Sibrian and Marsh were involved in a bitter court trial.