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A few questions. What USDA climate zone are you in? http://planthardiness.ars.usda.gov/PHZMWeb/
Is there a large tree in the area that might have similar foliage? Any spines on it? When you crush a leaflet, is there a discernible aroma?
The foliage is pinnately compound, so it looks much like Fraxinus sp. However, the foliage is alternately arranged along the stem - Fraxinus sp. are opposite in arrangement - so it must be something else.