A320
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Inflight Event / Encounter CFTT / CFIT
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Took Evasive Action
Human Factors
We were approaching Las Vegas flying the TYSSN3 arrival. At approximately 30 miles out we were cleared direct to SHAND and descend 8000 ft. A short time later we were cleared for the visual approach to 25L. The auto pilot and auto thrust were engaged and both pilots had Terrain on ND selected ON. Estimating our path to be approaching SHAND on a 300 heading; we discussed flying over the obstacle noted to be 3700 ft on the approach plate and selected 4900 as the altitude for SHAND as published; ensuring we would have more than 1000 ft clearance above the posted obstacle prior to joining the localizer for 25L. We noted how the terrain on ND feature did not display any obstacle in our path. We observed the radar altimeter decreasing and expected that to be our approach to the 3700 ft obstacle. The radar altimeter began decreasing rapidly and we heard a 'Terrain' warning quickly followed by a 'Pull up'. I immediately initiated a climb at TOGA thrust climbing approximately 1000-1500 ft on the same heading. As I recall; the warning sounded once and did not repeat. The FO advised ATC of our climb and subsequent level off and I believe I heard the controller mention the vectoring altitude in that area to be 5000 ft. We quickly reinstated the automation and joined the localizer for 25L.  Extending gear and flaps early we were able to rejoin the published glide path and our approach was 'stabilized' prior to 1000ft AGL so we continued to an otherwise normal landing. To be candid; I understand what triggers the terrain warning but I am uncertain why it triggered in this situation; as I thought we had accounted for the terrain in our approach path by selecting an altitude providing 1000 ft+ clearance. I would be speculating to suggest any other reason as I honestly am not sure. I can say with certainty that recent training on terrain events resulted in what we perceived to be an unquestioned and virtually instantaneous response to the warning once realized.
[Report narrative contained no additional information.]
A320 flight crew reported receiving a terrain warning on the TYSSN3 Arrival into LAS.