East Boulder Ditch


East Boulder Ditch

Established: April 1 1862

Priority Number: 5

Acres under ditch: 1115 originally

Water Source: South Boulder Creek


Almost 90% of East Boulder Ditch shares are owned by Xcel Energy today. Xcel uses East Boulder Ditch to fill Valmont Reservoir. They also transport other shares of water which they have bought from Dry Creek #2, Jones and Donnelly, and Enterprise Ditches, through East Boulder Ditch and into Valmont Reservoir.

East Boulder Ditch was also known as Pancost Ditch in its early days. Charles S. Pancost was an early Valmont farmer and probably helped construct the ditch. Pancost grew prize-winning wheat and started a vineyard.

Pancost also built the first recorded reservoir along South Boulder Creek sometime around 1863. Originally, the area was probably a swampy slough, which he enlarged and filled with East Boulder Ditch. Pancost Lake had a decreed water right for 93 acre feet, which would have made it about the size of Viele Lake. Pancost used the reservoir for raising “sun-fish” which he sold to miners, turning a tidy profit.

Pancost Lake is now buried under Leggett-Owens Reservoir, and is part of the Valmont Lakes complex. The lake has been expanded several times and has gone by many names over the years: Pancost Lake, Owens Lake, Leggett Reservoir, Harlow Reservoir, and now Leggett-Owens Reservoir. This challenged Boulder’s premier map-maker, Henry Drumm, as you can see in his 1926 map. He had a hard time fitting all the names and decrees in.

East Boulder Ditch traverses the hills surrounding Sombrero Marsh on three of its sides. Seepage from the unlined earthen ditch recharges the groundwater and flows down into the marsh, replenishing its wetlands.


East Boulder Ditch is “ground zero” for the Preble’s Meadow Jumping Mouse. The banks of the ditch boast the highest endangered mouse densities in Boulder County. This has presented a big problem for the ditch company: they are caught between a mouse and a hard place.

Ditches require constant maintenance, to keep the channel clear and to be able to transport water safely. However, it is very difficult to comply with the Endangered Species Act, and perform regular ditch maintenance at the same time. Without maintenance, ditches eventually fill and become unusable. The mouse habitat would disappear. But the maintenance itself can damage habitat and mice. Stay tuned, as this conundrum continues to play out in Boulder.

Map courtesy of Carnegie Branch Library of Local History.

< Previous Page | You are here: Home > Our Ditches > East Boulder Ditch | | Next Page >