A1. Ruined Nave

One of the statues in this area has an inscription with a date on it: this is likely to prompt groups that otherwise wouldn't have given any consideration to the calendar at all to ask the question "What year is it now?" If you'd rather not overly concern yourself with such matters you may want to remove the inscription, or at least the date portion, from the statue in area A1b. Otherwise, you decide upon a date--or at the least, a year--at which the campaign starts. Suggestions over on the Paizo forums suggest setting this around 4709, but if you have run other campaigns in the setting, you may wish to adjust this accordingly to where you wish to fit the adventure path in your time-line.

As far as skill checks for this area go: -

A1a.
A DC 10 History, Nature, or Streetwise identifies Pale Mountain in the bas-relief.
A DC 15 Religion identifies the manner of depiction is similar to the depiction of saints.
A DC 22 Religion identifies Vardishal.

A1b.
A DC 16 Perception check locates the secret door to A11. Opening the door without clearing the foliage from behind it requires a DC 14 Strength check.