Cosmiccharlie, Why are rivers and creeks no good? I heard from someone recently that if an area has flooded, then the morels won't fruit for a few years in that location. This seems counter to your suggestion of checking in flats and flood plains. Flood plains, by definition, flood. What's your take?
Is there any difference in terms of soil drainage? For example, some flood plains I am looking in stay pretty wet for a while after rains - they don't stay flooded, but they stay moist, as the soil retains the water for a good while. Compare that to a gentle slope with tulip poplar (still a moist environment), which although protected from sun, has pretty good drainage. Both sites have poplar and ash present.