Where are the salt rocks on time tangled island?

They are on the roof of Thomas Jefferson's house (7 o'clock, 1776 AD). When you return the rocks to 1387 AD, go to the Timbuktu Inn (far right) where you can get the Declaration of Independence for Jefferson.

In 1776 AD, jump up on the Graff House window ledges until you get all the way to the top. The rock salt (a tan bag of white rocks) will be on the roof.