Near the aqueduct bridge. I include the leaf picture to show how much the leaf helps in identification. You can see the leaves are directly opposite each other (instead of alternate). Also they have toothed edges. The really distinctive thing about them is that in addition to that central dividing line (the midrib), they have two prominent veins running somewhat parallel to the midrib. That seems to be a consistent characteristic among sunflowers. This variety is only 2-5 feet tall. Native. Aster family.
Thin-leaved Sunflower (Helianthus decapetalus)