Here's how Travis himself described them in 1908:
"Playing the twelfth hole at Garden City the other day, I put my tee shot in the bunker to the right—where it usually goes—and in playing out, lodged the ball on the very apex of a conical mound about three feet high, which had stymied my approach. How the ball managed to stay there is an absolute mystery. I suppose I could try it a million times again, from any distance, and with any club, without getting it to stay right on the very pinnacle. And wonders did not cease there! From the top of that mound I holed the ball with a mid-iron! The hole is one hundred and eighty-six yards from the middle of the tee to the middle of the green. The tee is some twenty-two yards in depth, the theory of the hole being that a full shot is demanded, involving a carry of at least one hundred and sixty yards, the tee-plates being moved backward or forward, according to the wind. It is a very difficult hole. On either side of the green are large mounds, beautifully turfed, some five feet at the highest point, tapering down to nothing. Over these mounds a ball may be putted or pitched. Immediately in front, about ten yards from the edge of the green, is a very deep bunker with big sand piles on either side and a sand bunker semi-circling the green about 20 yards equidistant from the edge of the green. During the last Amateur Championship, this hole came in for a great deal of criticism, both favorable and otherwise, and was variously dubbed, the Camel; the Dromedary; the Goat; the Sea Serpent; the Sacred Cow; the Hog's Back; the Razor Back; the Gate of Hell; the Humps; the Hummocks; the Hillocks; Travis's trap; and Travis's travesty. As somebody very truly observed, a hole which lends itself so easily to so many names must have undoubted merits. It is one of the hardest holes I know of, anywhere."
From the early photos it is clear those mounds were not maintained at green height. They may have technically been inside the edges of the green, but it wasn't until later that the mounds themselves were maintained as part of the green.
The articles leading up to the 1906 changes discuss how undulations were going to be added to a few of the greens (the 12th being one of them). You can sense the author of your article's surprise at first seeing those "undulations" in person, and my read on what he wrote, in combination with the photographs and Travis' own description, is that these were not your normal green surface bumps or waves, but something completely different. The author even goes so far as to distinguish the 2nd green from the 4th, 9th and 12th, noting it as the only one of the four where the term "undulations" could be applied.
I think this distinction is important, and is a different approach from what was done by CBM et al a few years later when developing the short at NGLA. There, the contours in the green were clearly undulations within the green surface.
Sven