How the data is built, where it comes from, and how we keep it from going stale.
The dog policy for each of the 63 national parks starts from the National Park Service pet page for that park, linked on every park page. The permissive parks and every park where access varies trail by trail were checked individually. The parks that follow the standard Park Service rule are summarized from that consistent policy, with the official page linked so you can confirm the specifics.
State park summaries are written at the system level, since most state systems apply one general rule. We flag the stricter systems (California) and notable exceptions. Rules can vary park to park within a state, so each page links to the official agency and tells you to confirm the individual park.
Every page carries the date we last checked it against the source. National parks are re-verified on a regular cycle, and any reader-flagged change gets checked right away.
We don't invent trail counts, we don't fake hands-on testing we didn't do, and we don't bury the official source. Where a rule is a general policy rather than a park-specific detail, we keep the wording general on purpose.