This weed has always grown in our yard, but I never bothered to look it up because I assumed it was wild strawberry. The little red fruits seemed so distinctive. Yesterday, as I searched for a link to include with this post, I realized that the yellow flowers are all wrong. Wild strawberry should have white flowers. After reading more online and consulting my old wildflower guide, I now believe this is Indian Mock-Strawberry.
(I would love a little help with this one. Please comment with corrections or confirmation!)