Wow, I didn't even think of that. Bicycles...tall grass...violence. It all makes sense now!
Anyway, I wouldn't really recommend that field; it's not that it's necessarily a creepy field, since it's in a residential area near 3 different schools, but it's just not a particularly thrilling field to do stuff in because it's wild. The ground probably isn't very even and the grass is probably hyperallergenic. Just some things to consider.
Also, minors should remember that there's an 11:15 curfew in Milwaukie, so they shouldn't be leaving the dance any time after 11 unless they're leaving to go home.