Blue carbon storage in coastal vegetated habitats is an important component of the global carbon cycle. In 2018, shallow sediment cores were collected in five USGS study marshes located in Humboldt Bay, CA. The cores were collected within 2 meters of the marsh edge to characterize carbon storage in areas susceptible to marsh edge erosion. Two sediment cores were collected in each of the five study marshes (Mad River, Manila, Jacoby, White, Hookton) using an Ejkelkamp peat sampler (52 mm diameter). The sampler was pounded in the sediments with a heavy plastic mallet. This method produces little to no compaction because once inserted, the corer is rotated 180°, and a sample is collected adjacent to where it was driven into the ground. A total of 10 shallow cores (1-meter) were collected with one exception. At the Jacoby South (CoreID - JSF1) a sandy substrate limited the core depth to 50 cm. The cores were sectioned at 10 cm intervals in the field and placed in labeled, pre-weighed metal tins. The 10-cm core sections were transported on ice and held in cold-storage. The 10-cm core sections were weighed, dried at 50 °C for 72 hours, and then re-weighed. Bulk density was determined by dividing the dry weight by the core volume for each 10 cm section of core. Dried core sections were analyzed for percent organic carbon at the University of California, Davis Analytical Lab (https://anlab.ucdavis.edu/) using acid fumigation and dynamic flash combustion. Replicate samples were run every 10 samples to check for instrument drift and the lab detection limit for percent organic carbon was 0.02.