Southwest Environmental Information Network (SEINet). Various dates.
The SEINet is a clearinghouse database that allows simultaneous searching of the records of a large number of herbaria that have substantial collections in the southwestern United States and adjacent Mexico. Results can be displayed in various ways, including by download of a KML file viewable in Google Earth and some other software packages, with hyperlinks to the herbarium records. The hyperlinks give access to a variety of information, depending on the herbarium and the specimen. There are restrictions on the use and display of the data, which are detailed on the SEINet site.
Although it is a wonderful resource, the data on SEINet should not be interpreted as reliably showing the distribution of a taxon. Rather, they provide a useful guide. You should be aware, though, that some of these specimens are misidentified, erroneous with regard to any given database field, and may represent collections outside of the native range (e.g. arboretum specimens, cultivated or naturalized specimens). I have tried to minimize such errors prior to displaying the data on the Gymnosperm Database but it is a laborious process (which is why such errors persist in the first place) and confirmation of identification is usually impossible, requiring as it does inspection of the original specimens.