Oregon-Grape is the State Flower for Oregon. When the berries turn purple they do look like grapes. This photo I shot in Alton Baker Park in nice light. Wikipedia has information about the plant - http://en.wikipedia.org/wiki/Mahonia_aquifolium Note the reference to the similarity of the leaves to that of holly.

The root of the plant has some medicinal value. It makes a bitter herb that is effective in treating digestive problems.
See - http://health.howstuffworks.com/wellness/natural-medicine/alternative/medical-uses-for-oregon-grape-ga.htm