AT SEACLIFF BEACH, a battleship rusts away at the end of the pier and a sandcastle training camp has sprouted on the shoreline.

Instead of seagulls there are parents milling and clucking admiration. Children are the day laborers. They cluster in groups, fluttering around the beach with buckets and trowels: future contractors of America developing the most expensive real estate in the area, building for the posterity of the evening.

It's a country of barrel-shaped keeps surrounded by kelp gardens. You can tell where the lords live, and what real estate maybe a landed knight would have to settle for. The King and Queen occupy the centerpiece of the morning: a behemoth of towers and twisty stairs carved by an expert, maybe the "Manuel" who printed his name on the front. But a flier is placed beside the royal apartments, an ad for Manuel's Mexican food. "Thanks to our local business sponsor!" There was no Manuel in sight by the time the castle began to dry and crumble.

A family of teens and pre-teens pile sand for 10 minutes before they have enough to start carving out around 30 layers of a Mayan pyramid. But they start late, and soon state parks volunteers come to gather the borrowed trowels and five-gallon buckets. There are a lot of five-gallon-bucket-shaped castles

Notoriously unstable, each sand structure is an individual 2012. They face destruction from the waves, the wind, the sun, the girl lurking with an I-want-to-smash-something look in her eyes. A man talking about professional castle building mentions spraying the sand with a water and glue mix—which is like cheating nature, like duct-taping the joints of a 95-year-old arthritis patient.

But I forget that sand had such structural integrity, even sans glue. There are a lot of arches and stairs, and some clean work coming from nonprofessionals. Scalloped and more-or-less Corinthian arches are admired by passing guardians, beachgoers in Capri pants and sweatshirts.

A small dark-haired girl realizes that moats don't last. She'll pour water into the sand forever, and the sun will go down a hundred times before the beach stops drinking it in. A boy draws a heart in the sand around his girlfriend, a younger girl etches her name into a castle wall. Sandcastles are an exercise in mortality, and by the end of the day the elaborate engineering has all been abandoned and waits in crumbling piles for the ocean.

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