Generate the contour plot. LEVELS= specifies contour levels from 10 to 90 at 20-unit intervals. AUTOLABEL= turns on labeling, and CHECK=NONE turns off collision checking so the maximum number of contour labels can be displayed. HAXIS= and VAXIS= assign AXIS definitions to the plot. LEGEND= assigns the LEGEND1 definition to the plot. 
proc gcontour data=reflib.clay2;
   plot y*x=pct_clay / levels=10 to 90 by 20
                       autolabel=(check=none)
                       haxis=axis1
                       vaxis=axis2
                       legend=legend1;
run;
quit;