The City of Simi Valley is a bedroom community in Eastern Ventura County. It is hot arid climate. Don't expect to see a lot of significant vegetation. There are trails at the edge of the city. The most common area for trail is the Rocky Peak area on the eastern edge of the city. As it name describes it has a large rocky surface. In addition to the Rocky Peak trail there are the Las LLagas Canyon, Chumash and Hummingbird trails. There is also a connector to the Corriganville which is an old Hollywood Western town. Just south of of Rocky Peak (although not in Simi Valley) is Santa Susana State Historic Park. The other area with trails in the south western corner. There is Mt McCoy which has a cross that you can hike to. At the southern end of First street is Challenger Park which has a number of trails and if you continue on, there are more trails in Long Canyon.
Simi Valley Parks and Recreation department has a web site with hiking information:
http://www.rsrpd.org/, this web site has information on the status of the parks affected by the Woolsey Canyon fire in 2018
http://www.rsrpd.org/simi_valley/trails/index.php
http://www.rsrpd.org/parks_and_facilities/index.php
and a small but really excellent map of the hiking trails:
http://cms4.revize.com/revize/ranchosimi/Parks%20and%20Facilities/RsrpdDistrictMap.pdf