I just found a dataset of trees in San Francisco, but I'm unable to determine the system used for the coordinates. Here are some samples:
Does this look familiar to anyone?
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This was down a bit in the comments at the link you provided:
SF uses State Plane, NAD 83, Zone 3, US Survey Feet. This coordinate system is used vs lat/longs as they have greater accuracy for smaller areas. We are looking at ways to convert this to lat/long to make it easier for consumers to use.