A mobile rig for use in lowering a string comprising joints of a conduit into a well is provided with a rig transporter comprising a motorized unit, a mast assembly, a pivotal connection on the mast assembly with respect to the rig transporter. At least one hydraulic arm is pivotally mounted to the rig transporter and the mast assembly operable to move the mast to an upright position and for lowering the mast to a substantially horizontal position for transportation. In one embodiment, a top drive is mounted in the mast which is raised and lowered with the mast whereby the top drive is transported in the mast in the substantially horizontal position.