You're pretty close to the Quad Cities. I'm pretty sure that you are zone 4. So...you are tallgrass prairie, and does this describe you?
"The Quad Cities are situated in a ecological transition zone between the Eastern Deciduous Forest and the Tall Grass Prairie and is, of course, dominated by the riparian
(read that: river)system.
A major factor in the economic success of the region is soil quality. As the glaciers of the last ice ages retreated, they deposited massive amounts of soil in Iowa and Illinois. The Canadian Shield was nearly scraped clean of soil, and Iowa was being dumped on by a carpet of 18 to 36 inches of rich black loess, our gift from the glaciers. And because of a combination of this rich soil, a moderate Continental (Long Summer) Climate, and one of the largest aquifers in the world, Iowa is one of the greatest agricultural producers anywhere."
http://lewis184.home.mchsi.com/my_home_town.htm
WE have 18-36 inches of "rich black loess" on our place. You drive one more hour south, to Chareston, and you get clay and rocks!
I would definitely go with the raised beds. You're a lot lower than my place, being close to the Mississippi, and my garden was FLOODED with too much rain last year. If I had had raised beds, I'm sure that my crop would have been much better in 2009. Especially since, the tomatoes that I grew around my cement cistern cover (where the land slopes away from my 100 year old farmhouse) did very well, while the regular garden drowned, because their soil drained.
As you know, any farmer with "bottom land" takes a gamble planting it--will it flood and lose the crop, or will it be dry and I'll have a great harvest?
Stop worrying and just "do it". Let us know how it goes.
