Past contestants have sculpted replicas of the Posey Tube, a Mayan temple and even Godzilla. Still others have opted for traditional castles with towering turrets, crenelated walls and saltwater moats.

What can be entered during the 43rd annual Sand Castle and Sand Sculpture Contest today is limited just by the imagination - and judging by past years, contestants will have plenty of it on display.

The free event at Robert Crown Memorial State Beach is an Alameda tradition. But it also attracts participants from throughout the Bay Area.

The rules are simple: Only material found naturally on the beach can be used, such as shells, stones and driftwood - and sand, of course.

Contestants can use shovels, hoes and spatulas to sculpt their work. They also can use buckets, milk cartons and other items to help shape forms.

Registration will be 9 to 11 a.m., and the deadline to finish sculpting is noon, when judging will begin. Entries will be based on design, detail, neatness and technique. Awards will be presented at 1 p.m.

The three contestant categories are ages 12 and under, ages 13 and older, and family.

The Alameda Recreation and Park Department, the East Bay Regional Park District, the Bayview Women's Club and the Alameda Youth Committee are sponsoring the contest.

The beach is located at Westline and Otis drives.