Cartoons were only on Saturday morning,
In the '70s at least, I think this was very much not true...we had at least two stations in our market that ran a full lineup of cartoons / other children's programming (Captain Cosmic usually ran Ultraman or other poorly-dubbed Japanese live action shows - think Power Rangers, except you didn't want to gouge your eyes out with a fork) from the end of Dialing For Dollars at 2:30 (coincidentally, both channels had DFD franchises that ran at the same time) clear through to 5:00P or 5:30P.
That said, that's one anecdote and maybe *I'M* the anomaly. Lawn Defenders, was this true elsewhere in the country?
Depends on the area. Most Large-Market cities in the Midwest (Cleveland/Detroit/Cincinnati) had at least one independent TV station (usually UHF) and a PBS station, but Toledo did not get their first independent station until the mid-80s (but then again, it wasn't too too hard to pull in the two Detroit indies).
If you look at some of the cities in the Mountain Time Zone (Colorado, Montana, New Mexico...) there were some smaller broadcast markets that still had stations which were affiliates to two or all three networks well into the 80's.
But for the most part, if your town or area was lucky enough to pick up an independent station off the antenna in the 60s & 70s, you were usually treated to reruns of some great shows of the past and some movies as well, with the better ones at night during prime-time.
Would've loved to have a VHS and a chance to tape the old reruns of the Allen Funt Candid Cameras back in the day -- one of the few non-game shows that are hard to find in reruns or on the internet anywhere, for that matter.