We believe these were Katydid eggs! See this similar photo of Microcentrum rhombifolium eggs from CSU: https://www.forestryimages.org/browse/detail.cfm?imgnum=5393465
Partly cloudy. About ten of these would do display flights each time the sun came out. In a remnant patch of native grassland in Denver.
Caterpillar observation:
https://www.inaturalist.org/observations/157979492