How do you turn your back yard into a green oasis when you live in the middle of the desert? For Grace and Mark, who live in Las Vegas, Nevada, it's been the impossible dream. Truckloads of topsoil have been absorbed by the arid desert soil. Grass has been hard to establish because of the heat and dry climate. And shade trees are impossible to plant because of calichi rock, a dense stone material that lies just below the soil surface and is common in drought regions of the country.