Salmonberries grow wild along the west coast of North America from northern California to Alaska. Raspberries are from the same family and would make a good substitute if you cannot find salmonberries.
For cupcakes: line 24 muffin cups with paper liners; fill 2/3 full with cake mixture. Bake in the preheated oven until a toothpick inserted near the center comes out clean, about 19 minutes. While still warm, poke holes into top of each cupcake with a fork; spoon salmonberry mixture over each cupcake.
For a sweeter, drier cake omit the topping. The topping is very tart. You can add whole salmonberries for embellishment.