Heat oven to 375°F.
Toss nectarines, berries, sugar, juice and cornstarch in large bowl.
Spoon fruit mixture into 8 x 8 x 2-inch square dish.
In same bowl mix flour and brown sugar. With fingertips, mix butter into flour mixture until crumbly. Sprinkle over top of fruit.
Bake in 375°F oven 50 to 60 minutes, until bubbly and browned.