For much of the way, Imperial Highway is signed as State Route 90. A de facto freeway portion of the route in Yorba Linda is also known as the Richard M. Nixon Parkway. The portion in Los Angeles County is located about one mile north of, and runs parallel to, Rosecrans Avenue.
Are areas of your lawn bumpy and uneven? When you walk across these areas does the soil sink or feel soft? If so, some type of soil dwelling critter is probably the cause. During winter the activity of moles, earthworms, and mole crickets can cause mounds and tunnels in lawns that result in uneven or rough patches. To fix these problem areas you must first diagnose which critter is causing the damage. Earthworms.
Minimize traffic on the mound, both human and animal, to avoid soil compaction. Do not exercise pets or stake pets on septic mounds. Never drive a car or other vehicle across the mound or mow when the soil is wet. Compacted soil can lead to soil erosion and impedes the flow of air around the system. In winter, activity on a mound can cause frost to penetrate resulting in freezing problems.