On Oct. 4, the Arroyos & Foothills Conservancy succeeded in preserving three acres of open-space land in the Altadena foothills. The land, which had been slated for a five-house development, is part of a 21-acre property in Rubio Canyon that was offered to AFC in July.

The acquisition brings AFC closer to its goal of preserving the canyon in its entirety, setting it aside for wildlife, hikers, birders, and enthusiasts of the scenic Mount Lowe Railway, which once passed through the canyon. It represents a major milestone in that effort, as these three acres were the most susceptible to development.

“This is a critical piece of land, and a major victory for local conservationists,” said John Howell, AFC’s executive director. “We still have a ways to go to preserve the entire canyon, but this is a big step in the right direction.”

In acquiring the land, AFC met a deadline to receive a price significantly below the appraised value.

L.A. County Supervisor Michael D. Antonovich was instrumental in the effort to preserve the land. So were the Mountains Recreation and Conservation Authority and the Santa Monica Mountains Conservancy, as well as Joe Edmiston, the executive director of both agencies.

Private donors also played a crucial role. Those donors include Ninarose Mayer, a 15-year docent at the Eaton Canyon Nature Center who gave $10,000. Ms. Mayer was responsible for a major donation that helped AFC acquire 20 acres in the canyon in 2009.

To date, AFC has preserved 23 of the canyon’s 41 acres. With the help of the local community, it hopes to acquire the remaining 18 acres by the end of the year to meet a second “best price” deadline. Preserving the entire canyon would protect a wildlife corridor, close one of the remaining gaps in the popular Altadena Crest Trail, open new trails into the mountains, and make it easier to access existing trails.