Colo. Rev. Stat. § 38-1-109
Any person not made a party to such proceeding may become such by filing a cross petition at any time before the hearing, setting forth that he is an owner or has an interest in the property sought to be taken or damaged by the petitioner and stating the character and extent of such interest. The rights of such person shall thereupon be fully considered and determined. Except for such cross petition, there shall be no written pleadings on the part of any party to the proceeding, but, at the hearing provided for in section 38-1-105, the court shall hear and dispose of all objections that may be raised touching the legal sufficiency of the petition or cross petition or the regularity of the proceedings in any other respect. In case any person or corporation at any time or in any manner succeeds to the right of any party in the subject matter of the proceeding, such proceeding shall not abate thereby, but such person or corporation, upon motion and upon proof of the fact of such succession, shall be substituted for such party as a party to the proceeding.
C.R.S. § 38-1-109