Valley Oak (Quercus lobata), also known as California White Oak. Valley Oaks grow only in California, generally below 2,500 feet elevation. They are the largest of all oak trees in North America, rising more than 100 feet above the ground, with trunks 6 or 7 feet in diameter. Trees with 3 to 4 foot diameter trunks are only 150-200 years old. Mature Valley Oaks can produce up to a ton of acorns in a good year. The acorns were the Yokuts Indian main food staple, mixed with other types of acorns to improve taste, ground, leeched of tannins and made into a mush, cake or flat bread.