Yes, there is a duty to create an inventory - not only of just the valuable items. You additionally need to create an initial accounting, and interim accounting, and a final accounting. The appraisal suggestion is not a legal duty but a good suggested practice. The inventory and accounting do have time limits attached to them and I would highly suggest that you seek out an attorney to assist you. Again, the PR should be disclosing inventory and accountings to beneficiaries.
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.
A personal representative has a legal duty under the Colorado Probate Code to file an Inventory of estate assets with the Court within 90 days after the estate opened and the personal representative is appointed. The Inventory should show all property of the estate and values for all property as of the date of death. These values can be ascertained in a number of ways, including an appraisal. However, an appraisal is not strictly required. If you are an heir or beneficiary of the estate, you have the right to see what is in the Court's file. If an Inventory has not been filed on time or if the Inventory appears to be incomplete or in error, you have the right to ask the Court for a hearing to determine any issues. I would suggest you contact an Elder Law attorney with Probate experience to assist you.
Nothing in this posting is intended to, or does it create an attorney-client relationship. Further, it is NOT legal advice, it is for informational purposes only. If you wish advice specific to your situation, you may contact me independently and ask for a consultation.
Agree with the above answers, but wanted to add a few points. You must prepare an inventory of assets within 90 days of appointment as PR. While you are not required to file it with the court or automatically provide it to all beneficiaries absent their request, it is probably a good idea to do so in most cases. You are required to send an Information of Appointment to all heirs/devisees within 30 days of appointment. You certainly don't want to be trying to hide or undervalue anything. An appraisal is not necessary for all assets, but may be a very good idea for certain types of assets (for example, real estate appraisal @ date of death, and rare items or collections).
Look to the C.R.S. 15-12-7xx's for information on your duties as PR. If you have any doubt about what you need to do, hire a probate attorney to advise you as PR. The expense can be paid out of the estate and will be well worth it.