Mary Cain wins women's 1500m final for second-straight year.
The teenage sensations will square off in February.
The 25-year-old Californian has the fourth-fastest time in the 800m this year.
Star miler Mary Cain flashed a smile on the Mondo track.
Men's, women's 800m winners triumph in quick fashion on the final day of the USA Outdoor Track & Field Championships.
She's only 16 years old.
There's a good chance for a new American record there.
It was the United States' first distance gold medal.
She was ranked #1 in the world in the 1500m last year.
It's the first and only indoor all-nighttime meet.