They were flying quite high over a lake, with deep wing beats, and quick maneuvers:
Their silhouettes were dramatic against the sunset clouds:
At times they looked like falcons, other times like kites:
A few times they came quite close. If you look carefully, in the next image you can see a white wing bar near the tip of the right wing:
I'm guessing these Common Nighthawks (Chordeiles minor) were in the midst of their migration to South America.
If you aren't familiar with them, nighthawks are in the nightjar family (Caprimulgidae) and are related to Whip-poor-wills and poorwills. This is a good time of year to watch for them. In New England, the Connecticut River Valley provides good opportunities for seeing nighthawks migrating at sunset. (I saw and heard Common Nighthawks over our house in Sebastopol when we first moved to California, and they have been observed on Bodega Head.)
Wish them a good journey!