Square-headed wasps (subfamily Crabroninae), as you can probably guess, are named for their large and square heads. They are active, solitary wasps that mostly hunt adult flies to stock their nests with. Nests are typically located in dead or rotten wood (logs, stumps) or hollow stems. This genus is widespread in the US and you can often find the adults on flowers.
Photo by: Glenn Marangelo on 6/26/21 in the National Bison Range near Moiese, MT