Fleece is king here, as is dressing in layers. The weather in March can be a bit unpredictable — bright sunshine one minute, thunderstorms the next. So just be prepared for a bit of everything.
I wouldn’t suggest going down to Oneonta Gorge it in spring unless you are in waterproof clothing. If 50 degrees is cold for you, than that water is going to be downright frigid. We were just at our local river the other day, when it was 60+ degrees outside, and my hand got really cold just reaching in for a rock. The temperature also tends to be a lot colder back in Oneonta Gorge. Generally, this is only a hike I would suggest doing on a hot summer day, otherwise you risk hypothermia pretty fast. The water will be at least waist deep.
However, you can hike up Oneonta Gorge a bit without getting so wet. There are also LOTS of other stunning waterfall hikes in the area that don’t require getting so wet, and if you head a little further east, depending on how warm the spring has been, you can also catch some stunning wildflower displays at places like Rowena Crest and Mosier.