Web Soil Survey - Home
Find your place here and it'll tell you what is going on on top of the hill. Sounds like you have a soil type change. Also some info on how well it'll hold roads and structures.
I would think 3" rock would be hard to keep in place. I made some silt dams out of 12"+ rip rap one year they were carried away in next rain. I've had better luck with straw bales and drive a stick through them. Just leave a crack between the bales to let hard rains through. Or else it could try to cut a new ditch.
You've made good progress. Looks like a nice place.
Got the soil figured out. I don't know how the heck they got all of those soil types mapped properly, but the map almost spot on with where the soil actually changed. The soil at the top of the hill is "Bunkum silty loam clay". It didn't say anything about compaction, but says it's somewhat poorly drained. I attached the spec sheet.
It's too late on the 3" rock. I already put it down. Wish I would've read your post prior to heading out today. Oh well, hopefully it turns out OK.