Cut a notch in a lime wedge, then run the lime around the rim of a glass. Dip the edge of the rim into a plate of the salt.
Place all ingredients in a cocktail shaker with 4 ice cubes and shake until cold.
Strain the margarita into the glass with the salted rim. Fill the glass with clear ice and serve.
Pitcher (8 servings): Place 1 ½ cups tequila, 1 cup beet juice, 1 cup orange juice, 1/2 cup Cointreau or Triple Sec, 1/2 cup lime juice and 1/2 cup simple syrup in a pitcher. Add 3 handfuls ice and stir until cold.