Abstract: A corner leg assembly comprises two grooved mating elements divided longitudinally which when held together form the female groove portion of two dovetail joints, one on each side facing laterally 90 degrees apart. One of the corner elements is a substantially triangular corner leg having perpendicular outside surfaces and parallel lengthwise L-shaped grooves on a 45 degree inside surface. The second element is a clamp block which includes opposite-facing L-shaped side grooves corresponding (being the mirror image thereof) to the grooves on the corner leg. The clamp block is affixed down the middle of the corner leg along the inside surface by one or more clamping fasteners such as a screw or bolt which passes through the clamp block. By turning the fastener(s), the clamp block may be loosened or removed to vertically adjust a laterally-extending panel or rail member.