Utah Code § 50-2-6

In all actions brought under this chapter it shall be sufficient to prove that a trust or combination as defined herein existed, and that the defendant belonged to it, or acted for or in connection with it, without proving or producing any article of agreement, or any written instrument on which it may have been based, or that it was evidenced by any written instrument at all. The character of the trust or combination alleged may be established by proof of its general reputation as such.