For the Crust:
Combine graham cracker crumbs, sugar, cinnamon, salt and butter in large bowl. Press evenly into bottom of 9x13-inch pan. Chill for at least 1 hour.
For the Filling:
In medium bowl, mash raspberries and blackberries together with sugar, vanilla and salt until berries are mostly broken up. Cover and chill for 30 minutes.
Pour water into small sauce pan. Sprinkle gelatin over top and let sit for 5 minutes to soften gelatin. Place over low heat and warm until gelatin is completely melted. Remove from heat and sit until no longer warm to the touch but still liquid, about 5 minutes.
In bowl of stand mixer fitted with whisk attachment, or in large bowl with hand-held mixer, beat heavy cream just until it starts to thicken. Add gelatin to cream in a steady stream, then beat to stiff peaks.
Add chilled berry mixture to cream mixture and gently fold together with large spatula. Spread on top of graham cracker crust and chill for at least 2 hours. Slice and serve chilled.