Erigeron karvinskianus or the Mexican Daisy is a good ground cover that will scramble over rocks or uneven ground.
It is a perennial with lax stems and narrow hairy leaves and produces a mass of small open faced daisy type flowers in white,pink and red most of the year round in warmer climates.
It can be invasive if not controlled but it is reputed to be a very good mosquito repellent.
Very good for the leading edge of a herbaceous border or rockery.