Rancho Posolmi was a 1,696-acre (6.86 km2) Mexican land grant in present day Santa Clara County, California given in 1844 by Governor Manuel Micheltorena to Lupe Yñigo. The name refers to Posolmi village of the Ohlone. The grant encompassed present day Moffett Field in Sunnyvale.
Robert Walkinshaw was a native of Scotland, who came from Mexico in 1847 to take charge of the New Almaden Quicksilver Mine for Baron, Forbes and Company, a British trading firm.
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 Posolmi was filed with the Public Land Commission in 1852,  and the grant was patented to Thomas Campbell, Robert Walkinshaw, and Lopez Yñigo in 1881.
In 1931, 1,000 acres (4.0 km2) were purchased by Bay Area communities and sold to the military for $1, to be used for an air base, later named Moffett Field.
- Ogden Hoffman, 1862, Reports of Land Cases Determined in the United States District Court for the Northern District of California, Numa Hubert, San Francisco
- Diseño del Rancho Posolmi
- Early Santa Clara Ranchos, Grants, Patents and Maps
- Laurence H. Shoup, Randall T. Milliken, 1999, Inigo of Rancho Posolmi: The Life and Times of a Mission Indian, Malki-Ballena Press, Novato, California, ISBN 978-0-87919-142-9
- United States. District Court (California : Northern District) Land Case 410 ND
- Report of the Surveyor General 1844 - 1886