Thank you. I'm not a geologist or anything, but I think most of the mountain ranges on the US west coast are relatively young, leading me to believe these sand dunes are probably small and growing. As the mountains wear down, I'd imagine these dunes will expand a great deal. I'd love to see massive ones! Death Valley does have some big ones, but they aren't easily accessible. The Eureka Dunes are some 3 miles long and 1 mile wide and over 700 feet tall. I do plan on visiting them one day. :)