Over the past decade, the northeastern Pacific has witnessed repeated and severe heatwaves that have profoundly impacted the functioning and productivity of marine and adjacent terrestrial ecosystems. However, there remains considerable and long-standing uncertainly regarding NE Pacific climate variability prior to 1900 CE and the extent to which recent extremes are atypical in a longer-term context. Here, dendrochronology techniques are applied to growth increments of the long-lived Pacific geoduck (Panopea generosa) to develop a 277-year chronology, which is combined with tree-ring data to reconstruct sea surface temperatures of the NE Pacific over the past five centuries. This temperature history is dominated by interdecadal variability of apparently tropical origin as well as a sharp 20th century warming trend culminating in a new “ultra-warm” regime beginning around 2014. These same tree-ring chronologies are also critical for dating trees killed in landslide- and fault-formed lakes. The deaths of trees in these “ghost forests” yield new insights into the landscape-level impacts of the 1700CE Cascadian Subduction Zone earthquake and reveal the scale and timing of a late Holocene multi-fault megaquake underneath what is now Seattle, Tacoma, and Olympia, WA.