I don't think you can see Mather Pass from the East side because Mather is lower than the crest. The only place on the crest lower than Mather is Taboose Pass, and the ridge extending WSW from Cardinal Mountain would block the view of Mather thru Taboose. I hope the following photos illustrate this--click on them for high res versions.
This photo shows Upper Basin and Mather Pass from near the JMT/Taboose Pass trail intersection. Mather Pass is the low point about 3/4 from left to right. The Palisade group is visible thru the pass.
The photo above is the second of four frames in the panorama below. Taboose Pass is to the right behind the treed ridge. The mountain with colored rock at far right is Cardinal Mountain. Mather pass is the low point at the panorama's center, and the ridge extending WSW from Cardinal would block the view north to Mather.
This photo shows Mather Pass as seen from the north from Upper Palisade Lake. Mather is the gap right of center backdropped by clouds. Mt. Bolton Brown is at left.
Well, this doesn't explain what you were looking at, but I hope you like the photos.
