From the City of Jax website and JaxPsychoGeo: Marjenhoff Park is just east of San Marco. Alex Marjenhoff, a local resident who served on the South Jacksonville City Council, initiated efforts to develop the park from a swamp in 1929. The old South Jacksonville City Hall where he served still stands, on Hendricks Ave at Cedar St in San Marco. Despite the '29 market crash and Great Depression, the city managed to fill the marsh, creating a small lake with an island, and planted trees and other plants to beautify the grounds. The cache is hidden among the remains of this shrubbery. You can still spot Marjenhoff's distinctive house roof across from the park, which frequently floods in storms, trying to return to its native wetland state.