The longevity of textured geomembranes (GMB) widely used as base and slope liners is rarely studied. The variability of the thickness and defects on the surface of co-extruded textured GMBs result in non-uniform mechanical properties across the GMB roll. Therefore, the effect of texturing on the stress crack resistance (SCR) of unaged and aged high density polyethylene geomembranes is studied herein. The fracture plane of broken geomembrane specimens in notched constant tensile load (NCTL) test is investigated using the environmental scanning electron microscope. The comparison between the crack growth rate estimated by fracture mechanics laws and the SCR estimated in NCTL test shows that the defects and discontinuities on the textured geomembrane surface are the main source of variability of the NCTL results.