Black Walnut - Identifying where root starts?

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I was reading about the importance of making sure the root flare is above ground and noticed one of the black walnuts I had planted appeared to be "straight like a post".

In an attempt to surface the root flare, I took a horse brush and brushed away soil around the base until I surfaced a small lateral root (not visible in this picture).

However, I was reading that young black walnut trees often do not have a well defined root flare, and think I may have gotten too zealous with my base clearing. According to stark bros, black walnuts should have their root transition identified by color, and I think I see a color transition in this picture where I have marked it.

Was I correct to surface the larger lateral root, or did I go too deep and should return soil to the level indicated?

Uploading again with a better picture.

I was reading about the importance of making sure the root flare is above ground and noticed one of the black walnuts I had planted appeared to be "straight like a post".

In an attempt to surface the root flare, I took a horse brush and brushed away soil around the base until I surfaced a small lateral root (not visible in this picture).

However, I was reading that young black walnut trees often do not have a well defined root flare, and think I may have gotten too zealous with my base clearing. According to stark bros, black walnuts should have their root transition identified by color, and I think I see a color transition in this picture where I have marked it.

Was I correct to surface the larger lateral root, or did I go too deep and should return soil to the level indicated?