“ Because, under the Colorado law, the appointment of the commissioners is a step in the suit after the filing of the petition and the service of summons upon the defendant. It is an adversary judicial proceeding from the beginning. The appointment of commissioners to ascertain the compensation is only one of the modes by which it is to be determined. The proceeding is, therefore, a suit at law from the time of the filing of the petition and the service of process upon the defendant. ”

“ It requires the filing of a petition setting forth the authority of the plaintiff to acquire the property in that mode, the purpose for which it is sought to be taken, a description of the property, and the names of all persons interested therein, who are to be made defendants and brought into court by the service of a summons or other process, as in other cases is provided by law. ”