The St. Johns series consists of sandy soils that have a black A1 horizon and light gray A2 horizon less than 30 inches thick, a Bh horizon that is black in the upper part and dark reddish brown in the lower part, and a C horizon of pale brown sand. Total thickness of the A horizon is less than 30 inches.
Soil reaction ranges from extremely to strongly acid in all horizons.
Texture is sand or fine sand in all horizons except the Bh horizon includes loamy sand and loamy fine sand. The A2 horizon has hue of 10YR, value of 5 to 7, and chroma of 1 or 2, or is neutral with value of 5 to 7. Some pedons have a continuous layer about 1 inch thick at the top of the Bh horizon that contains about 4 or more percent organic matter. Vertical or horizontal tongues or masses or both of gray to light gray sand are in the Bh horizon of some pedons. The B3 horizons has hue of 10YR, value of 3 to 6, and chroma of 3 or 4, or hue of 7.5YR, value of 3 or 4, and chroma of 2 or 4.