Shelltown is a neighborhood in San Diego, California, located within Southeast San Diego. It is bordered by National City to the south, Interstate 5 and Barrio Logan to the west, 43rd Avenue to the east, and Gamma Court and the neighborhood of Southcrest to the north. Prior to the 1980s the northern border of Shelltown was National Ave and ma…Shelltown is a neighborhood in San Diego, California, located within Southeast San Diego. It is bordered by National City to the south, Interstate 5 and Barrio Logan to the west, 43rd Avenue to the east, and Gamma Court and the neighborhood of Southcrest to the north. Prior to the 1980s the northern border of Shelltown was National Ave and many residents still consider that the northern border. Naval Base San Diego, an industrial park, and some commercial buildings are located just outside the western border of Shelltown along Main Street.