There is a tremendous amount of Open land in Carlsbad as you head east. If the city is declared built out, it’s because the local people/government would like it that way. If you are traveling the areas mentioned between Melrose and El Camino Real and various other areas, there is a ton of open space. I am also thinking around Faraday/El Camino Real area there is a lot of open space. I took my kid up to the Calavera Hills Park for a Pony game the other day, and took the back way up (Cannon which becomes College) and there was space around that area as well.