Tarragon Tequila Palomas

Name: Tarragon Tequila Palomas
Ingredients: 1/4 cup (2 oz./60 g) kosher salt; 1/4 cup (2 oz./60 g) sugar; 1/4 cup (1 1/2 oz./45 g) grapefruit zest; 4 grapefruit wedges; 2 cups (16 fl. oz./500 ml) fresh grapefruit juice; Leaves from 4 fresh tarragon sprigs, plus sprigs for garnish; 1/2 cup (4 fl. oz./125 ml) fresh lime juice; 2 oz. (60 ml) agave syrup; 1 1/2 cups (12 fl. oz./375 ml) blanco tequila; 6 cups (3 lb./1.5 kg) ice; 1 1/2 cups (12 fl. oz./375 ml) club soda, plus more as desired; 8 grapefruit wedges