Choose a record, examine the returned list using BerkeleyMapper and "Related searches". Records from the first of each month are likely to be special: many were generated by database errors (April 1901 being stored as April 1 1901).Sort by collector | Sort by distance | Sort by date
Obviously, people sometimes collect at sites more than 60 miles apart on the same day (a degree of latitude is sort of 60 nautical miles, a degree of longitude varies according to latitude). Even in the 1890's a collector could hop off a train at a whistle stop and botanize until the next train came along.
These entries are linked to a complete list of records for the collector and day. Use the sorting functions and BerkeleyMapper to find the source of the error. The date may be wrong; the coordinates may be wrong; the collector may be wrong. Note that the "Related searches" at the bottom of the detail display lets you search for records near a displayed record.