Air Carrier Pilot reported while on the MARCS 1 STAR and RNAV (RNP) 22 approach into SAT the GPWS Warning activated just as the pilots noticed a nearby ground object. The pilot stated the object is poorly marked on the approach chart and should be corrected.

Narrative

The ATIS at SAT was advertising the visual approach to Runway 22. Since the flight was planned using the MARCS 1 Arrival I loaded the RNAV (RNP) 22 Approach in the box since it had BRAUN (IAF) as a common fix with the STAR and briefed a visual approach backed up by the RNAV (RNP) 22. Upon reaching the MARCS fix at 13;000 feet approach gave us a 180 degree heading and a descent to 7;000 feet. I slowed the aircraft to get the flaps to 1 to help with the descent. Approach subsequently gave us a 270 degree heading and a descent to 4;000 feet and then 3;000 feet and I selected flaps 2. At this point we were inside of the BRAUN intersection and the current heading would bring us close to the ZALYO (IF) fix so we extended [the radial] off of the ZIGDA (FAP) fix. With the runway in sight approach cleared us for the visual to Runway 22. While monitoring the plan view I saw that once inside of ZALYO I could descend to 2;100 feet and proceeded to do so. A few miles from ZIGDA I selected 1;700 feet and selected the approach mode. I was trying to get to altitude so that the approach would capture (FINAL APP). As we were descending both the F/O and myself were looking at a surface mining operation and associated tower/crane and commented about how low it looked and almost at the same time we received an [GPWS] obstacle call. I clicked off the auto pilot and climbed back to 2;100. We were still a couple miles from the ZIGDA fix and had Runway 22 in sight the entire time. We finished configuring the aircraft and proceeded uneventfully to landing. We were both surprised with the obstacle call as an obstacle is not readily evident on the [chart] plan view. It's not until you look really close that short of the UWEZY fix there is an obstacle. However it is partially hidden by two arrows corresponding to two different approach courses. This is an approach that can bite you pretty quick especially if given vectors and then cleared a visual; especially if backing it up with the RNAV (RNP) 22. (If given vectors the RNAV (GPS) Y Runway 22 would be a better choice). By extending [the radial] off of ZIGDA the only altitude associated is 1;700 feet which then puts the aircraft too close to the obstacle. Another item is that the ZIGDA fix is only 2.8 miles from the runway so the expectation of 1;500 feet AGL [a standard glide path] and 5 miles from FAF to runway is not there.Add a note to the company pages highlighting that the ZIGDA fix is only 930 feet above and 2.8 miles from the runway. Change how the obstacle short of the UWEZY fix is accounted for - possible a note on the plan view. For myself; I am going to put the Runway/field in the fix page and put a 5 mile ring and then ensure that I am at 1;500 feet AGL (3-to-1[ratio]).