Monrovia Hillside Preserve provides 1,416 acres and 4.5 miles of trails for the community, per the City of Monrovia's website here: https://www.cityofmonrovia.org/your-government/recreation/wilderness-preserve
However, the City's website is woefully outdated since the Sleepy Hollow entrance has been blocked off and marked with "No Trespassing" signs. In addition, two other entrances are surrounded by "Residents Only" parking signs. The Ridgeside entrance is not marked at all and is only accessible via an easement at 873 Ridgeside Drive (stay on the pavement). I definitely get the vibe that the locals did not really support this preserve, unlike other Foothill neighborhoods such as Glendale and La Cañada that take great pride in preserving the beauty of their natural wildnerness areas.
In addition, the Preserve is pockmarked by parcels of private lands. You will be walking along a trail and all of a sudden there's a sign advising you that you may not proceed because you will be on private land. Very disconcerting.
Worst of all is the complete take-over of non-native plants. An invasive plant/native plan restoration program seems to be absolutely nonexistent here. This is all the sadder because the Preserve is home to a federally-endangered flowering plant. Lots of invasives, unfriendly neighbors and challenging parking are big problems; however, the land and views are stunning. Monrovia has a gem here but does not know what to do with it. read more