The St. Vrain Creek corridor comprises the river channel and riparian habitat starting at Steamboat Mountain (N. St. Vrain) and Hall II (S. St. Vrain) and ending near N. 119th St. in Longmont. This area offers a notable concentration of wildlife, unique biodiversity, and vital habitat to “species of special concern.” The stream corridor features cottonwood‐willow riparian groves, cliff faces, and grassland habitats. According to Boulder County’s Critical Wildlife Habitat Descriptions, species of special concern that are known to occur here include golden eagle; bald eagle; plains topminnow; common shiner (state threatened); Iowa darter; stonecat; great blue heron; black tailed prairie dog; American beaver; and the endangered Preble’s meadow jumping mouse (see Critical Wildlife Habitat #7). Threatened Ute ladies’-tresses (a type of orchid) are also found in the area. Recently confirmed sightings of the state threatened Northern river otter are an encouraging sign of the improving health of this ecosystem, which should not be jeopardized by industrial activities in the area. The Critical Wildlife Habitat Descriptions document lists other species of special concern as potentially occurring in this habitat.

The Boulder County Comprehensive Plan (BCCP) includes a number of maps that illustrate biodiversity across the county. The BCCP Critical Wildlife Habitats & Wildlife Migration Corridors Map [PDF] reveals that the St. Vrain Creek corridor is considered a critical wildlife habitat, described as “an area of unique habitat which has a crucial role in sustaining populations of native wildlife and in perpetuating and encouraging a diversity of native species in the county. The area may be significantly productive habitat or particularly vital to the life requirements of species that are critically imperiled or vulnerable to extirpation.” The BCCP Environmental Conservation Areas Map  [PDF] designates the St. Vrain Creek corridor as a Riparian Habitat Connector, which is an area of “wildlife movement adjacent to relative unfragmented waterways which provides connectivity among Environmental Conservation Areas.” Also informative are the BCCP Preble’s Meadow Jumping Mouse Conservation Areas Map [PDF] and the BCCP Wetlands & Riparian Areas Map [PDF]. In Best Management Practices for Wildlife Corridors, Beier et al. note that best practices for streams in corridors entail protecting or restoring a continuous strip of native vegetation at least 200 meters (656 ft) wide along each side of the channel.

The Survey of Critical Biological Resources in Boulder County, Colorado 2007-2008 [PDF] is an extensive report prepared for Boulder County by the Colorado Natural Heritage Program at Colorado State University. The “Saint Vrain Creek below Lyons” area is noted for its significant biodiversity. To address the problems posed by habitat fragmentation, the “Recommended Conservation Strategies” include recognizing the importance of larger, contiguous natural communities, to ensure that we do not lose species that have not yet been located (61).

Of course, the survey above precedes the 2013 flood. A more recent report created for Boulder County Parks and Open Space, the 2014 Riparian Inventory and Assessment of Post-Flood Conditions Boulder County Parks and Open Space Properties Boulder, Left Hand, and St. Vrain Creeks [PDF], claims that “Overall, flooding increased the potential for plant and animal diversity by creating new land forms, including new meanders and main channels, abandoned channels, side channels, point bars, and pools. Habitat for wetland plants in particular increased” (41). This underscores the need for an updated, post-flood survey of the entire area, which could reveal valuable new information about its current and potential biodiversity.

Bird studies

In 1997, two studies were conducted on birds in and around the property proposed for mining:

The report on breeding birds cites 60 species observed on the former Western Mobile, Inc. property, with 28 of those species definitely nesting on the property, 19 that may have nested, and 13 migrant or non-nesting summer visitants.

The report on birds of prey noted that bald eagles, red-tailed hawks, American kestrels, and great horned owls nest on the property where mining was initially proposed. In addition to potential nesting habitat for other raptors of special concern (golden eagle, northern harrier, and eastern screech owl), there is also potential foraging habitat on the property for at least five additional raptor species of special concern (golden eagle, ferruginous hawk, peregrine falcon, prairie falcon, and short-eared owl).

These 1997 reports are now two decades old. A new bird study is reportedly being conducted for Martin Marietta at this time, and S.O.S.V.V. community members look forward to reviewing and verifying the final bird study report(s).


At 562 species, Boulder County’s bee diversity is one of the highest in Colorado, and the St. Vrain Creek corridor provides important habitat for various kinds of pollinators. These species are key to the ecological balance in our region. As Kearns et al. note, “Loss of native bee species can lead to loss of native plants that rely on them for reproduction.” Riparian habitats are critical to the well-being of pollinators in the area, providing vital floral and nesting resources for a wide diversity of native bees. Dr. Adrian Carper is currently leading a team of researchers conducting a survey of native bees along the St. Vrain Creek corridor. They are studying the woody debris that bees require for their nesting habitat, and how its availability affects the abundance and diversity of cavity-nesting bees. As Dr. Carper stated in a recent presentation, “Open spaces are bee hotspots.” Let’s keep this important open space open.

Over the last two decades, the monarch butterfly population has declined by 90 percent. Monarchs pollinate many types of wildflowers as they feed on nectar. Milkweed—the only plant on which monarch butterflies lay eggs—can be found throughout the St. Vrain Valley. While Colorado falls between two of the main monarch migration paths, the region does host “strays,” and milkweed is necessary for their continuing survival.