UTM zones - west edge, overlap, v.mkquads

[Scott Wade]

  Can someone provide a quick lesson on the nature of UTM
  zones?  I thought there was some overlap between adjacent
  zones, with low eastings in one zone overlapping with the
  high eastings of the neighboring zone on the west.  True?

  Why I ask:  I need a vector layer of USGS quadrangle edges
  in a location that is on the west edge of zone 12.  If
  I run v.mkquads with a very low number for the west edge
  of the current region, v.mkquads fails with this message:

  Zone of the given point (zone: 11) does not match zone of the current window 12
  Can't go across UTM zones.

  This message is received with any west edge set to less than 218244.

  Oddly, the east side of the region seems to be extensible for quite
  a distance, with v.mkquads working fine with an east edge
  of, for example, 1500000.

  Theoretically, doesn't a UTM zone have a west edge of zero?
  And what's so magical about E218244?

  thanx

  ////\\\\////
  Scott Wade
  wade at zorro.cecer.army.mil