The maps on CalTopo show historical fire data, with perimeters color-coded by year along a yellow-to-red spectrum, where red typically represents the most recent fires (e.g., 2016–2020) and lighter colors indicate earlier periods, starting from 2000 or 1900, depending on the selected dataset. On the CalTopo.com site in the link below, users can choose between these timeframes via a dropdown menu. Each fire perimeter includes the year and incident name, though labels may require zooming in for smaller fires, and overlapping perimeters can make identification challenging. The fire history layer is updated annually, typically after the new year for the previous year’s data, using final perimeters recorded from sources like low-flying aircraft or ground personnel for high accuracy. These maps are integrated with CalTopo’s topographic layers, such as USGS topos or MapBuilder, allowing users to overlay fire history with terrain, trails, or other features for backcountry planning or analysis.
