A B757-200 flight crew experienced loss of left hydraulic system fluid and pressure. They declared an emergency; ran the QRH; and landed without incident.

Narrative

On descent from FL340 for approach to ZZZ; noticed 'Left Hydraulic Pressure' light on EICAS followed by 'Left Hydraulic Quantity' light. Pulled checklist out and began to follow procedures for 'Left Hydraulic Pressure.' Noticed rapid drop in hydraulic quantity to .35 fill. Secured pumps in accordance with checklist. Leak slowed but did not stop completely for approximately 4-5 minutes. With pump switches off; noticed fluid drop to stabilize at .15 fill. Captain briefed crew and passengers; advised Flight Attendants to perform cabin advisory; talked with Dispatch. Declared emergency and transferred flying control to Captain. Completed appropriate checklist for manual flap/gear extension. Briefed approach; reviewed performance for 20 degree flap landing; no left reverse; no nosewheel steering and contaminated runway. Landing and rollout were uneventful. Set parking brake with nosewheel on centerline. Of Note: We had no APU which complicated SAFE walkaround environment for Crash Fire Rescue team. Also tow in; also consideration for passenger comfort (no lights/heat with harsh outside conditions). Super tug brought over for tow; plug in for electrical power was listed as inoperative on tug. Secured left engine and agreed to leave right engine running. All Ground personnel briefed to be extra cautious when working in proximity of engine and aircraft. Of Note: Only on climbout; we noticed 'L Reverse Stow Switch' annotation. Notified Maintenance Control and was told to include in log write-up. He also relayed to us that this was probably an electrical switch problem.