Fossil ammonites from lower Cretaceous mudstones in northern California, which are supposedly 112–120 million years old and biostratigraphic index fossils, were sampled along with fossil wood buried with them. Fragments of two fossil ammonite shells and four pieces of fossil wood yielded easily measurable radiocarbon (14C) equivalent to apparent 14C ages of between 36,400±350 and 48,710±930 years for the ammonites, and between 32,780±230 and 42,390±510 years for the wood. Any contamination with modern 14C due to the sample environment and handling was eliminated by the laboratory's severe pre-treatment procedure. Any alleged contamination due to sample combustion or AMS instrument background was more than compensated for by the laboratory background of 0.077 pMC already having been subtracted from the reported results. The ammonite shells could not have been contaminated in the ground by replacement with modern carbonate 14C either, because they yielded almost identical 14C apparent ages as the wood buried and fossilized with them. It was concluded that the measured 14C is in situ radiocarbon intrinsic to the ammonites and wood when they were buried and fossilized. So once past conditions in the atmosphere and biosphere are taken into account, their true ages are consistent with their burial during the Genesis Flood only about 4,300 years ago, when the ocean waters washed sediments and ammonites onto the continents.