[4] When asked what land they wanted, the Coast Miwok chiefs chose 80,000 acres (324 km2) ranging from Nicasio Valley to the area surrounding Tomales.
[5][6] In 1844, Governor Manuel Micheltorena granted the 56,621-acre (229.14 km2) Rancho Nicasio to Pablo de la Guerra and John B.R.
In 1850 Pablo de la Guerra sold his 30,848 acres (124.8 km2) undivided share of the ranch to Henry Wager Halleck.
Halleck had arrived in California in 1847 as a lieutenant in the United States Engineers, accompanied by his friend, Lt. William Tecumseh Sherman.
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.