Looks more like an aster or daisy than fleabane. Typically had ~20 white petals with oval ends, moderately wide for their length, but close to each other. I'm thinking OXEYE DAISY, but they seem relatively rare along the Rim, whereas these guys were the most common flower I found today. Oxeye are hardiness zone 3-8, and this area is 6b-7b. You can also see layering of petals, as found on daisies.

https://www.wildflowersearch.org/search ... 37903.y=94