Here are a few places where Sandhill Cranes reliably spend the winter:
Woodbridge Ecological Reserve, California
Bosque del Apache NWR, New Mexico
Padre Island National Seashore, Texas
During migration (March-ish and October-ish) you could try Platte River, Nebraska.
You can easily find more through Google, or the birder grape-vine.
And! The websites that I used for research: