An A320 inbound to LAS was cleared for a visual approach to Runway 19L from the vicinity of GRNPA intersection. As they began their descent from 5;000 MSL they received an EGPWS warning.

Narrative

We were cleared the approach for Runway 19L just after GRNPA Intersection. This immediately caught our attention as it was a clear night and the terrain ahead (rising to 4;080 FT) was clearly visible. LAS Approach usually clears you for the approach later on the arrival and advises you to to turn final prior to the Stratosphere (about 3.5 mile final or so thus avoiding the terrain to the northeast). Being cleared the approach from where we were put the terrain directly between us and a five mile final.We decided to maintain 5;000 FT until passing over the terrain; as we started the descent out of 5;000 FT though; we got GPWS terrain warning. Since we were south of the crest of the terrain we thought we'd avoid the GPWS advisory; but once we started the descent; we got the advisory. We immediately began a shallow climb and the GPWS ceased. We continued to an uneventful landing. Although we were aware of the terrain; our descent was initiated too early resulting in the GPWS advisory and momentary warning. We could have avoided any potential conflict by continuing initially toward the final further south and turning final at an appropriate altitude and distance from the runway.