This study reveals the hidden carbon stored in forested wetland soils, highlighting the importance of accurately mapping these areas to understand global carbon storage. The Hoh River Watershed (HRW) in the Pacific Northwest of the U.S. contains 68,145 ha of forested wetlands, which are not included in current global soil organic carbon (SOC) maps. The study found that the total SOC stock in the HRW at 30 cm depth is between estimates from global SOC maps, with wetland SOC stocks being significantly higher than current wetland-specific SOC maps. The study estimates that the total unmapped or 'cryptic' carbon in the HRW is 1.5 TgC, which, when added to current estimates, increases the estimated wetland SOC stock to 1.8 TgC or by 482%. This highlights the vast stores of SOC that are not mapped and contained in unprotected and vulnerable wetlands. The study shows that forested wetlands, which are difficult to map due to canopy coverage and small surface area, contain high SOC stocks and play a critical role in the terrestrial carbon cycle. These wetlands contribute significantly to terrestrial carbon storage but are often overlooked in current maps. The study used a continuous probabilistic wetland identification metric to reveal significant amounts of unmapped SOC contained in potential forested wetlands and wet areas. This approach identified a nearly five-fold increase in the amount of SOC estimated to be contained in potential wetlands, mostly hidden under thick forest cover. The study also found that the SOC stocks in the HRW are significantly higher than those in current wetland-specific SOC maps. The results show that the spatially continuous WIP probability metric is a significant covariate for SOC when combined with surficial geology. The study emphasizes the need for improved wetland mapping to account for high SOC in forested wetlands and wet areas not contained in contemporary inventories. The findings highlight the importance of conserving Earth's carbon-rich ecosystems to meet the goals of balancing carbon sources and sinks for the Paris Climate Agreement. The study provides an adaptable approach that is informed by a continuous wetland identification metric which maps and reveals high SOC stocks driven by wetland potential on the landscape. This mapping revealed the vast stores of unmapped forested wetland SOC stocks or cryptic carbon compared to currently available wetland SOC maps. The study underscores the need for more accurate mapping of forested wetland extent and SOC stock to improve conservation of a valuable carbon sink that is underestimated with currently mapped wetland extents.This study reveals the hidden carbon stored in forested wetland soils, highlighting the importance of accurately mapping these areas to understand global carbon storage. The Hoh River Watershed (HRW) in the Pacific Northwest of the U.S. contains 68,145 ha of forested wetlands, which are not included in current global soil organic carbon (SOC) maps. The study found that the total SOC stock in the HRW at 30 cm depth is between estimates from global SOC maps, with wetland SOC stocks being significantly higher than current wetland-specific SOC maps. The study estimates that the total unmapped or 'cryptic' carbon in the HRW is 1.5 TgC, which, when added to current estimates, increases the estimated wetland SOC stock to 1.8 TgC or by 482%. This highlights the vast stores of SOC that are not mapped and contained in unprotected and vulnerable wetlands. The study shows that forested wetlands, which are difficult to map due to canopy coverage and small surface area, contain high SOC stocks and play a critical role in the terrestrial carbon cycle. These wetlands contribute significantly to terrestrial carbon storage but are often overlooked in current maps. The study used a continuous probabilistic wetland identification metric to reveal significant amounts of unmapped SOC contained in potential forested wetlands and wet areas. This approach identified a nearly five-fold increase in the amount of SOC estimated to be contained in potential wetlands, mostly hidden under thick forest cover. The study also found that the SOC stocks in the HRW are significantly higher than those in current wetland-specific SOC maps. The results show that the spatially continuous WIP probability metric is a significant covariate for SOC when combined with surficial geology. The study emphasizes the need for improved wetland mapping to account for high SOC in forested wetlands and wet areas not contained in contemporary inventories. The findings highlight the importance of conserving Earth's carbon-rich ecosystems to meet the goals of balancing carbon sources and sinks for the Paris Climate Agreement. The study provides an adaptable approach that is informed by a continuous wetland identification metric which maps and reveals high SOC stocks driven by wetland potential on the landscape. This mapping revealed the vast stores of unmapped forested wetland SOC stocks or cryptic carbon compared to currently available wetland SOC maps. The study underscores the need for more accurate mapping of forested wetland extent and SOC stock to improve conservation of a valuable carbon sink that is underestimated with currently mapped wetland extents.