SELECT "Date" FROM table_37992 WHERE "Site" = 'memorial stadium • minneapolis, mn' AND "Opponent" = 'northwestern'
What is the Date at memorial stadium minneapolis, mn, and an Opponent of northwestern?
CREATE TABLE table_37992 (
    "Date" text,
    "Opponent" text,
    "Site" text,
    "Result" text,
    "Attendance" text
)