Last year we found an area in the meadow that had a colony of these mining bees.
BugGuide IDed them for us. (You can find some of our images from last year by clicking on the IMAGE tab.)
We roped off a small area of the colony.
Last year the colony went inactive immediately when the sunflowers stopped blooming.
The species of sunflower is Helianthus simulans, which is quite closely related to Helianthus angustifolius.
We kept the vegetation low in the roped area.
No activity all year until now.
2 weeks ago, the first sunflower blossom opened in the meadow. Now the meadow is full of blossoms.
Each day the mining bee activity in our little plot grows.

John