Combine the lettuces. Roughly tear 8 cups butter lettuce leaves and 1 cup raddichio leaves and toss in a large bowl.
Add the toppings. Cut 3 peaches into slices and add to the lettuces with 1 pint blackberries. Add ¼ red onion slices, ¼ cup candied pecans, and ¼ cup feta cheese.
Mix the vinaigrette and dress the salad. In a small bowl, whisk ⅓ cup extra virgin olive oil, 3 tablespoons seasoned rice vinegar, 1 tablespoon sugar, 1 tablespoon fresh tarragon leaves, 1 teaspoon Dijon mustard, plus ⅛ teaspoon each kosher salt and black pepper. Pour the dressing over the salad, toss, and taste for seasoning. Add more feta cheese as desired.