Rancho Mallacomes (also called Moristul and Mallacomes y Plano de Agua Caliente) was a 17,742-acre (71.80 km²) Mexican land grant in present day Napa County and Sonoma County, California given in 1843 by Governor Manuel Micheltorena to José de los Santos Berreyesa. The grant was located in the Napa Valley, just north of present day Calistoga and consisted of Mallacomes or Moristul and Plano de Agua Caliente. Mallacomes comes from mountain chain Serro de los Mallacomes ( Mount Saint Helena) and included most of Knights Valley (previously known as Mallacomes Valley).