1000++ nests over the entire base path on a town ballfield. Photo 1 shows the area around 1st base bag. Photo 2 is a closeup of a portion of this same area. Photo 3 is home plate.

Greater number of nests observed in the clay-colored substrate on the base paths compared with the grey substrate on home plate and the pitcher's mound.

A few individuals of Nomada lehighensis were observed parasitizing the nests. See observation https://www.inaturalist.org/observations/213534760

This was part of a rare and fascinating "mass flight" of Red Admirals. Saw literally Hundreds of them in the same 1-1/2 acre area throughout this 1 day. They traveled north through the area, sometimes stopping on a plant but often just flying through.
The next day, only 2 were observed in the same area.
See also https://www.inaturalist.org/observations/213712198