Uplifted marine terraces on Santa Catalina Island, California, USA

Abstract

Abstract Marine terraces are widespread along California's coastline, including on all of the Channel Islands, with the possible exception of Santa Catalina. For over a century, the origins of subhorizontal surfaces and gravel deposits on Santa Catalina have been debated, with recent suggestions that Santa Catalina has no marine terraces and is subsiding. We mapped, measured, and described terrace deposits on Santa Catalina Island, including both in situ deposits and distributed gravel float. Rounded gravels and cobbles, locally pholad-bored, are present as float across low-relief surfaces in the Little Harbor area. We also mapped and described the Eagles Nest Gravels, an ∼8-m-thick package overlying a broad bedrock-cut platform at ∼200 m elevation and dipping 3.2° northward. The Eagles Nest Gravels contain rounded cobbles and boulders, many of which contain pholad borings. Two other platforms are inferred from concordant gravels with similar orientations but at lower elevations. Terrace deposits on Santa Catalina truncate underlying lithological units, including a narrow band of fossiliferous Miocene to Pliocene sands. Terrace deposits and gravel lag on Santa Catalina closely resemble older terrace deposits on other California Channel Islands. The terraces on Santa Catalina Island remain undated but document at least 200 m of net uplift, similar to the elevations of undated terraces on the other Channel Islands. While the timing of uplift of Santa Catalina is unclear, analysis of terrace deposits in the Little Harbor area confirms their marine origin and settles the debate regarding the presence of marine terraces on Santa Catalina Island.