Button Rock
Button Rock is an earth dam located in Boulder County, Colorado, built in 1969. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Button Rock
The primary purpose of Button Rock is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by City Of Longmont (huson, Ken) (local government). It impounds the North St. Vrain Creek near Lyons.
The dam stands 214 feet tall and stretches 925 feet across, creates a reservoir covering 222 acres, has a maximum storage capacity of 20,400 acre-feet, and collects water from a drainage area of 99 square miles. Completed in 1969, the structure is well into its service life at over 50 years old.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 08/12/2022.
At 214 feet, this dam is taller than 99% of all dams in the United States.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Colorado dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Colorado |
| County | Boulder |
| Nearest City | Lyons |
| River/Stream | North St. Vrain Creek |
| Coordinates | 40.21706, -105.36705 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 214 ft |
| Dam Height | 210 ft |
| Dam Length | 925 ft |
| Year Completed | 1969 (57 years old) |
Storage & Hydraulics
| NID Storage | 20,400 acre-ft |
| Max Storage | 20,400 acre-ft |
| Normal Storage | 16,080 acre-ft |
| Surface Area | 222 acres |
| Drainage Area | 99 sq mi |
| Max Discharge | 29,000 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | CITY OF LONGMONT (HUSON, KEN) |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 08/12/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CO00171 |
| Federal ID | CO00171 |
| More Info | State Dam Safety Program |