Bob,
Great page on this famous Zion landmark. There is a discrepancy between the elevation you list as 6,550 feet and the topo map which shows 80-foot contours. John Kirk's website lists the interpolated elevation as 6,680 feet - see: http://www.listsofjohn.com/PeakStats/Climbers.php?Id=21743
Thanks, Tracy. I think my elevation is based on my GPS reading, and you know those can be off a bit. I probably never bothered checking the map carefully or mistakenly read the contours as 40-foot intervals (that's more likely what I did) and therefore thought the reading was pretty accurate since an interpolated measure would be 6540.
Anyway, it's corrected now, and Checkerboard Mesa just got 130' higher!