The first known inhabitants of San Carlos were the Ohlone Indians. Ohlone is the name that has been given to the many related groups of Native Americans living along the coast between Monterey and San Francisco.

They hunted deer and small game and relied largely on the bay and ocean for food. The Ohlone used tule reeds that grew near the bay and along the many creeks in the area to build their homes and canoes.
Since food, clothing, and shelter were plentiful, the Lhamshin tribe lived a peaceful life, preferring trade to war.

Life abruptly and dramatically changed for the native people of the San Francisco Peninsula, when Spanish military and civilian settlers arrived to establish military garrisons (presidios), Franciscan missions, and civil settlements (pueblos). By 1810, introduced diseases, forced labor, and efforts to indoctrinate the indigenous peoples into an alien society and religion led to a tragic destruction of the Ohlone way of life in this "time of little choice"