These oaks have been in the ground one year in USDA hardiness zone 9. The root system already has grown to the where the man and women are standing. Note the faint white line on the ground from the trunk to where the man is standing. This is a root that we painted white.
Roots on live oak can grow 8 feet in EVERY direction in the first year after planting in zones 8 through 11. Roots in cooler climates grow slower. For example expect about 12 inches of root growth in zones 2-4; 18 inches in zones 4-5; 24 inches in zones 5-6; 36 inches in zones 6-7; 48 inches or more in zones 7-8.