1987 - Present Backbone maps:

Summer-2009 Early-2008 Spring-2006 Summer-2005 Late-2003 Early-2003 Jul-2002 Mar-2002 Oct-2001 Jul-2001 Qwest Jul-2001 Sprint Jan-2001 Qwest Jan-2001 Sprint Nov-2000 Qwest Nov-2000 Sprint Early-2000 Late-1999 Mid-1999 Late-1998 Mid-1998 Early-1998 Late-1997 Mid-1997 Early-1997 Mid-1996 Late-1995 Early-1995 Late-1994 Mid-1994 1993 1992 1987