Helianthus pauciflorus. Usully has darker disk flowers but occasionally yellow.

Lance-Leaf Coreopsis.

Lance-Leaf Coreopsis is one I first looked at because I have seen it in this meadow before, however the petal shape doesn't seem to match as its petal edges are more jagged and irregular whereas Helianthus pauciflorus petal more closely match those in my sample, smooth and pointed.