Answer: I think you are describing pokeweed, Phytolacca americana (decandra), a fairly common large wild plant with berries which color in late summer to early fall. Here are some images of the plant in various stages of growth: http://www.csdl.tamu.edu/FLORA/imaxxpht.htm . Unfortunately, I could not find a photo of the P.americana berries when ripe. Instead, here is a photo of the ripe berries on it's cousin Phytolacca sandwicensis, http://www.botany.hawaii.edu/faculty/carr/nat20.htm -- they look very similar. Please be aware that the plants are considered poisonous.
Q&A Library Searching Tips