Look for amaranth in between rows of corn. Be careful if you do harvest from a cornfield. The farmer may have used an herbicide to deal with the amaranth.
The leaves and seeds of amaranth are both edible. Be aware that amaranth does contain a scant amount of oxalic acid. In theory, cooking (blanch and shocking for example) does remove some of the oxalic acid content.
That reminds me. There are around 70 different classifications of 'amaranth'. When you search for amaranth, use the scientific name "amaranthus". Palmer amaranth, or pigweed, grows just about everywhere.
Now that you have Amaranth (Pigweed), what do you do with it?
Gather the seeds. Cook until soft. Spread on a cookie sheet and bake at 250 for 30 minutes or until dry. Grind to a powder. Store in an airtight container in a cool, dry place. Use it as a flour substitute.
Cook the seeds (1 cup seeds to 1 cup water) until soft. Add fruit, butter or syrup to make a warm cereal.
Eat the young leaves as a side dish. Blanch and shock before eating. The leaves can be bitter.