Answer

In Jain tradition, Shikharji / Sammed Shikharji is an extremely sacred Siddha Kshetra where 20 Tirthankars attained Nirvana.

However, the specific idea that “when kaal ends, Shikharji hill goes down into the earth and gold covers it” is not something I can confirm as a clearly established Jain teaching.

So the accurate answer is:

Sorry, I can only provide information that is clearly established within Jain tradition.

Explanation

Jain Dharma does teach that:

• Time moves in endless cycles of Utsarpini and Avasarpini.
• Worldly conditions rise and decline according to kaal.
• Sacred places like Shikharji have deep spiritual importance because of the Tirthankars’ Nirvana.

But the statement about the mountain physically going into the earth and being covered with gold may be a local belief, oral story, or regional tradition, and I should not present it as scriptural fact unless it is clearly verified within accepted Jain tradition.

Takeaway

Shikharji’s main significance is not gold or physical change, but its status as a sacred place connected with moksha, vairagya, and the Nirvana of Tirthankars.