In Focus
Built to Last: The Dam that Paved the Way for Crowley Lake
By Lesly Figueroa
About 760,000 years ago, a massive volcanic eruption formed the Long Valley Caldera, a pivotal geologic formation that paved what would become the Long Valley Reservoir. In Mono County along the historic Highway 395, the reservoir is surrounded by the picturesque natural beauty of the snow-capped Sierra Nevada mountain range to the west and the volcanic geologic wonders of the Glass Mountains to the east.
A volcanic caldera is a large cauldron-like hollow bowl formed from when a magma chamber empties during an eruption. This geologic gift created a natural basin, making it an ideal location to construct the Long Valley Dam at Owens Gorge, a steep, 10-mile canyon where the Owens River already naturally flowed.
In 1940, LADWP completed the Long Valley Dam, a critical component to the Los Angeles Aqueduct (LAA) system. The dam created what is now known as Long Valley Reservoir or Crowley Lake, Los Angeles’ largest storage reservoir. Officially named in honor of Father John Crowley, a beloved Catholic priest known as the “Padre of the Desert,” the reservoir covers an area of 8.2 square miles and has a capacity of 183,248-acre feet.
Everything that is built from the ground up will eventually face the test of time. Century-old infrastructure requires upgrades to ensure its continued strength and reliability. Improvements to the Long Valley Dam were essential to keep our system strong and resilient. By investing in the longevity of the reservoir, we extend the lifeline of Crowley Lake, honoring its role in community recreation, environmental stewardship, water resiliency, and preserving the legacy of one of the Eastern Sierra’s most iconic landmarks.
Long Valley Dam Undergoes Critical Safety Improvements
In late spring of 2025, LADWP began repairs to Long Valley Dam's emergency slide gate system. This system is used as a low-level outlet for the Long Valley Reservoir in the event of an emergency to prevent overtopping of the dam. The slide gate acts like a large door that allows for the release of water that is then connected to a stem, a long rod that can move the gate up or down, while the operator is the mechanism used to control the system. Crews completed the work with minimal issues thanks to detailed and coordinated planning efforts. The emergency slide gate, stem, and operator were officially commissioned on October 1, 2025, one month ahead of schedule.
The repairs overall improve safety by enabling a faster draining of the reservoir in case of damage or signs of potential failure. The emergency slide gate and stem, commissioned in 1941, failed in 2017 during annual operation of the gate in preparation for dam inspections performed by the California Department of Water Resources (DWR) and Division of Safety of Dams (DSOD). When the stem and operator failed, Water Operations Division's Aqueduct Section, Northern District, designed and built a temporary lifting apparatus to operate the gate during an emergency. This temporary lifting measure remained in place until the installation of a permanent replacement. The emergency diversion tunnel, where the gate resides, sits at the bottom of the Long Valley Reservoir, over 115 feet below the above ground operator that rests on the dam.
Construction began on April 7, 2025, with the goal of completing the work before November, when snow season typically begins. All work for the improvements were planned and constructed by LADWP crews. Water Operations Division's Aqueduct Section, Northern District, led the design and construction management, with support from Water Engineering and Technical Services' Mechanical Design and Geotech Design groups, who focused on the emergency slide gate and coordination of the required DSOD approvals. Construction was performed by the Northern District's Bishop Construction and Pump Shops. Water Operations' Metro Section Property Management group assisted with applying the protective coating of the gate during construction.
"The work carried out by our crews and engineers demanded strategic planning and precise execution, ensuring every detail was accounted for in the process. Workspace in the tunnel and tolerances around the stem are very tight, so significant time was spent to carefully plan out the work, sequencing and contingencies. Improvements to the work areas such as platforms, lighting, communications, as well as fabricating parts, helped ensure the project went as smoothly as possible."
Jennifer Barrick, Manager of Aqueduct Northern & Southern District Engineering
Planning for Safety Improvements and Challenges Encountered
Effective water management planning efforts are done strategically and are responsive to the unique environmental conditions experienced in the Eastern Sierra. Balancing infrastructure needs with climate variability can challenge construction plans, often requiring adaptive strategies and innovative solutions.
The Long Valley Reservoir is inaccessible during the winter months due to snow, therefore creating a limited construction window to complete the work. Water levels in the reservoir must be low enough for work to be performed safely, and during high runoff seasons, construction could not be performed and was delayed.
During high runoff years, a full reservoir might be viewed as a positive sign. However, it can pose serious operational challenges due to the design of the emergency spillway infrastructure, which is where the water is released to prevent overtopping of the dam. At Long Valley Reservoir, the emergency slide gate is used as the low-level emergency outlet. The slide gate is accessed via a wye-branch off of the spillway tunnel. This design means that if Long Valley Reservoir fills up and exceeds the spillway elevation, water flows into the spillway tunnel where crews may be working. For reservoirs like Long Valley, a high runoff year can set back planned improvements in the spillway or emergency tunnels due to concerns about worker safety.
Another challenge of the project was threading the new stem down through the existing 115 foot shaft to match up with the new gate location. Due to the design of the original slide gate, there was no access to monitor the stem to determine if it was damaged during installation. Sections of concrete were removed to connect the stem to the gate, 115 feet below the dam operator. LADWP crews performed this work methodically and with precision to ensure successful installation.
"The skills required to design and execute these construction improvement projects are a testament to the courage and dedication of our crews and engineers. Their efforts are instrumental in preserving the incredible engineering legacy of the Los Angeles Aqueduct system.“
Eric Tillemans, Aqueduct Manager
The access and procurement of specialized materials and equipment was also a considerable challenge, given the critical nature of this work. It was important to source materials to ensure longevity and durability to last at least another 80 years.
The emergency slide gate is a critical part of the reservoir outflow system, and the upgrades were essential to ensure safe, reliable water releases during an emergency, and overall preserve the long-term functionality and operations of the Long Valley Reservoir.
Crowley Lake, Integral to the Community
Long Valley Dam, and the impressive engineering behind its design created Crowley Lake, a vital resource that reflects the uniqueness of water in the Eastern Sierra and the City of Los Angeles. The reservoir is an iconic symbol of community, recreation, and water management. The Long Valley Reservoir provides water management for the Owens River and a reliable source of water for the City of Los Angeles and clean power generation plants in the Gorge. Recreational activities at Crowley Lake are abundant, and the lake serves as a popular fishing spot for locals and visitors alike, recognized as an “Angler’s Paradise.” Every year in April, Fishmas marks the start of the trout fishing season, where boaters and anglers cast a line and celebrate the joy of fishing and tradition. Casting a line in Crowley Lake is a tribute to the importance of the reservoir to the region and a nod to the ongoing work of LADWP crews who protect and manage this vital resource today.
A Legacy Worth Protecting
Father John Crowley's, the “Padre of the Desert,” lives on in the Eastern Sierra and is memorialized through Crowley Lake and multiple regional landmarks. Father Crowley was determined to improve the economic development of the region by boosting tourism. He was critical of water infrastructure in the region, but was committed to ensuring the vitality of the community. Prominent figures like Father Crowley teach us that desert valleys are not barren wastelands but rather rich with life, history, and beauty. The nearly century-old infrastructure of the Long Valley Dam and the recent upgrades highlight the preservation of that legacy while paving a way for a long-lasting future.
If you find yourself in the Eastern Sierra, surrounded by towering mountain ranges, ancient volcanoes or alpine lakes take a moment to breathe in the crisp fresh air and be reminded of the long history of the region. The volcanic activity that created unique geologic formations, the priest that revered the Eastern Sierra, and the crews that built the Los Angeles Aqueduct. When you gaze out to Crowley Lake filled with boaters and anglers, they’re a reminder of the past and a vision into a future that values tradition. Cast a line, and who knows, maybe luck is on your side, and you’ll land a Sierra Grand Slam, catching all four species of Eastern Sierra trout in one trip.
For more information about LADWP in the Eastern Sierra, visit LADWP.com/EasternSierra.
