Ring widths, scans of samples, and ancillary data from Sequoia sempervirens (coast redwood) trees and stumps at Fort Ross and Gualala, sampled for dendroseismology in 2021–2024

Sequoia sempervirens (coast redwood) trees were sampled for a dendroseismological investigation along the North Coast Section of the San Andreas Fault, and the data were fully analyzed, interpreted, and discussed in a journal article and supplemental material (Carroll et al., 2025). Here, were provide data associated with this work: 1200 dpi resolution images of tree cores and stumps, raw ring width measurements for living trees and stumps with associated crossdating categories, standard tree and location chronologies with sample depths, and descriptions of tree cores. Please refer to the journal article and supplemental material for full details, supporting material, and context.
Tree ring samples were collected at two locations: Fort Ross Historic State Park (Fort Ross) and Gualala Redwood Timber Company (Gualala). Eleven living trees (8 at Fort Ross, 3 at Gualala) were climbed with ropes, and 5-mm-diameter increment cores were collected at various positions on the main and reiterated trunks. Skilled sawyers took plunge cuts from 23 Sequoia stumps at Gualala, sometimes taking multiple pieces from one stump.
Ring series were scanned at 1200 dpi. Child folders include scans of living tree and stump samples. Pencil marks guide crossdating, but final dating is expressed in the ring width files with associated crossdating categories. Ring widths were measured to 0.001 mm precision using WinDendro software (v.2009b, Régent Instruments Inc., Québec, Canada). Crossdating proceeded using a multi-pronged approach combining visual assessment of marker years with correlation analysis, fully detailed in the journal article. Due to the complex nature of crossdating Sequoia, every year was assigned a level of crossdating confidence following previously defined protocol (Carroll et al., 2014; Carroll and Sillett, 2023) with categories of high and moderate confidence to distinguish sections with some ambiguity. For example, moderate confidence applied when missing ring(s) were known, but the placement may be in several positions. Undated rings were either 1) bound by dated rings, allowing the number of missing rings and total radial growth to be determined or 2) not bound by dated rings, as may occur for inner rings.
File “Tree Ring Widths_Carroll et al 2025.xlsx” lists ring width measurements in microns for 126 series from 11 living Sequoia trees at Fort Ross and Gualala. Crossdating categories are color coded, and these categories must be considered for proper use of the data. Measurements with no highlighting are dated with high confidence, measurements highlighted in orange are dated with moderate confidence, measurements highlighted in red are undated. Undated rings do not correspond with calendar years. Zeros (0s) reflect missing rings. Zeros (0s) in undated (red) sections reflect a known number of missing rings but unknown annual placement. Green highlighting reflects broken or crumbly sections. File "TreeRingWidths.json" provides these same data in a more easily machine-readable format. File “Tree Core Logsheet_Carroll et al 2025.csv” lists descriptions associated with these series.
File “Stump Ring Widths_Carroll et al 2025.xlsx” lists ring width measurements in microns for 37 sections from 23 Sequoia stumps at Gualala. Crossdating categories are color coded, and these categories must be considered for proper use of the data. Dated or partially dated paths are listed in columns B to S and correspond with calendar years in the first column. Measurements with no highlighting are dated with high confidence, measurements highlighted in orange are dated with moderate confidence, measurements highlighted in red are undated (and do not correspond with calendar years). Zeros (0s) in undated (red) sections reflect a known number of missing rings but unknown annual placement. Completely undated paths are listed in columns U to AM, do not correspond with calendar years, and are listed in descending order (from outer ring toward center). File "StumpRingWidths.json" provides these same data in a more easily machine-readable format. Descriptions of each stump sample are found in the supplementary material of the journal article.
Rings dated with high confidence were used to generate inter-annual reference chronologies for each tree and locations. First, tree-level chronologies were produced using only series dated with high confidence. Series were standardized via ARSTAN software (Cook, 1985) using a cubic smoothing spline with a 50 % frequency cutoff at 32-yr (32-yr spline) to remove geometric growth trends and low-frequency variation. Standard (STD) tree chronologies were then combined into location chronologies with no further detrending using a biweight robust mean (Cook and Kairiukstis, 1990). File “Tree and Location Chronologies_Carroll et al 2025.csv” lists the standardized ring indices for each tree and location with associated sample depths.