My random thoughts...
1. I believe 7 Bridges was a dump site that was scouted out by the perp.
2, The perp had plenty of time to find the perfect spot (and I think it was very familiar area for him). Harvest was completed 1 month ahead of schedule this year because of the drought. Most fields were harvested by mid-October at the latest. The number of farm workers would depend on the size of the equipment used and the size of the fields. (Each square mile of land is 640 acres.) (On average I'd estimate 3 workers per field....one in the combine, one in the chase cart, and one driving semi....this can certainly fluctuate by farmer). When I look at this photo
http://wcfcourier.com/news/evansdal...ion_12862912-cdd5-11e1-a9b3-0019bb2963f4.html
the first thing I notice is that the ground to the right of the road has tillage already done. Because of the amount of debris on top I think this was planted to corn this year. On the left side of the road I believe it was planted to soybeans because there is no tillage. I don't see any NH3 tracks in the bean field....nor do I see them in the corn field. Whoever farms this ground on both sides of the road may be waiting to make sure the ground temp is right before applying nh3.
3. Having a car from another county come down the road while harvesting isn't that unusual. Many hunters start a month ahead of time watching for deer/pheasant activity. Pheasant hunting started Oct 27 and it's lawful to hunt the ditches in Iowa....which many do. So to have people come down the road to the entrance of this park wouldn't be unusual....especially if they were known in the area to hunt. The farmer may think the person is checking for wildlife, when in reality the person was checking to see the pattern of people activity.
4. Temps just started to cool down, so 7 Bridges keg party activities may be starting to slow down (Wapsie Valley Jr & Sr High is 5 miles drive .... and I'm pretty sure the student body would use this as a party site. It's remote, but it's also a good place because if you get raided you've got plenty to hide behind, then walk home later).
5. Farmers are done with tillage, high schoolers are looking for warmer places to party, snow should be coming soon (like within the next 24 hrs) and that is why I think the drop happened within the last few weeks. MOO