Preheat oven to 350°F. Grease a 9-inch square baking pan.
In a large bowl, beat butter and brown sugar until creamy. In a separate bowl, whisk together flour, baking soda and salt. Add flour mixture to butter mixture and mix until crumbly.
Stir in 2 cups oats until combined. Press half of the oat mixture into the prepared pan. Top with berries.
In a small bowl, combine remaining 1 cup oats and 3/4 cup sugar; sprinkle over berries.
Bake 35 minutes or until golden brown. Cool before cutting into bars.