The Clojure and ClojureScript readers do not currently track the column number when reading forms, only line numbers.
((juxt :line :column) (meta #'identity)) => [1351 nil]
Several components could be improved by tracking column information:
Patches Clojure's LispReader and other components of the compiler: http://dev.clojure.org/jira/browse/CLJ-960
ClojureScript's reader will need a similar patch, but that's not required to enable SourceMaps.