You need to merge the data and convert it to "long" format:
data Heights;
input site height;
datalines;
1 10
2 12
3 17
4 6
;
data Diameters;
input site diameter;
datalines;
1 3.4
2 5.6
3 12.1
4 8.3
;
/* merge data and convert from wide to long format */
data Want;
merge Heights Diameters;
by site;
Group = "Height "; Value = Height; output;
Group = "Diameter"; Value = Diameter; output;
run;
proc sgplot data=Want;
hbarparm category=site response=Value / group=Group groupdisplay=cluster;
run;