Yoiks...that's what I was afraid of...Thanks so much for your response. This is the best I could come up with. The example is for memorial day which is celebrated on the last monday of may...
<?
$lastMondayDifference=abs(date("w",mktime(0,0,0,05,31,$viewYear))-1);
$memorialDate=date("Y-m-d",mktime(0,0,0,05,31-$lastMondayDifference,$viewYear));
?>
If you can see of a way to make it nicer, please let me know and thanks again for your help.