[12] The flat top has an oval shape and a surface area of 6 by 12 nautical miles (11 km × 22 km; 6.9 mi × 13.8 mi);[13] it is characterized by a limestone dome on the summit, buried beneath sediments; in turn a volcanic hill is buried within the limestone dome.
[14] The top of the seamount has a hummocky appearance which has been interpreted as a sediment cover[15] and its southeastern sector has a bank-like shape that resembles that of an atoll.
[19] Apatite,[20] basaltic sandstone containing hypersthene,[21] clay,[22] limestone, manganese crusts,[23] manganese oxide, phosphorite[24] and lithified carbonates have been found on Cape Johnson Guyot;[25] some carbonates of biogenic origin have been altered by apatite.
[26] Globigerina ooze is also found on the seamount[27] and can reach substantial thickness; such accumulations might be formed by ocean currents.
[37] The Cretaceous fossils[38] Actinostroma pacifica,[39] Astrocoenia dietzi,[40] Brachyseris montemarina,[41] the caprinid rudists Caprina mediopacifica, Caprina mulleri[42] - including a detailedly described holotype of the latter[43] - and Cardita sp.,[44] Lophosmilia fundimaritima,[45] Montastrea menardii,[46] Nerinea sp.