Preheat the oven to 400 degrees F. Line a 12-cup muffin pan with paper liners. Whisk the flour, baking powder, baking soda and salt in a large bowl. Whisk the granulated sugar, vegetable oil, sour cream, eggs and almond extract in a medium bowl; stir into the flour mixture until just combined with small bits of flour remaining. Stir in the nectarines and blueberries.
Divide the batter among the muffin cups, filling them three-quarters of the way. Sprinkle the almonds on top, then sprinkle with coarse sugar. Bake until the muffins are golden and the tops spring back when gently pressed, about 20 minutes. Let the muffins cool 5 minutes in the pan, then remove to a rack to cool completely.