See SQL WHERE condition at https://github.com/communitysnowobs/cso-api/blob/master/src/observations/query.js#L17
Having that filter makes it impossible to obtain some of the data in the CSO database and therefore reduces the value of the CSO observations API for QA/QC'ing the CSO database. Also, it assumes the elevation data are perfect, and that no valid data could be associated with negative elevation values generated by the Google Elevation API.